Method and apparatus for channel estimation for radio link between a base station and a relay station

ABSTRACT

A method is provided for receiving a downlink signal at a downlink reception entity in a wireless communication system. Downlink control information is received by demodulating a Physical Downlink Control Channel (PDCCH) in a first resource block (RB) pair within an RB bundle by using a first Demodulation Reference Signal (DMRS) in the first RB pair. Further, downlink data is received by demodulating a Physical Downlink Shared Channel (PDSCH) in one or more second RB pairs within the RB bundle by using a second DMRS in the one or more second RB pairs. The second DMRS is used based on an assumption that a same precoder is applied to the one or more second RB pairs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/246,883, filed on Apr. 7, 2014 (now U.S. Pat. No. 9,439,180 issued onSep. 6, 2016), which is a continuation of U.S. patent application Ser.No. 13/640,700, filed on Oct. 11, 2012 (now U.S. Pat. No. 8,730,903issued on May 20, 2014), which is the National Phase ofPCT/KR2011/002941 filed on Apr. 22, 2011, which claims priority under 35U.S.C. 119(e) to U.S. Provisional Application Nos. 61/414,881 filed onNov. 17, 2010, 61/405,230 filed on Oct. 21, 2010, 61/327,067 filed onApr. 22, 2010, and 61/327,068 filed on Apr. 22, 2010. The contents ofall these applications are hereby incorporated by reference as fully setforth herein in their entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a radio communication system, and moreparticularly, to a method and apparatus for channel estimation for radiolink between a base station and a relay station in a radio communicationsystem supporting multiple carriers.

FIG. 1 shows a relay node (RN) 120 and User Equipments (UEs) 131 and 132located in an area of one base station (or eNodeB or eNB) 110 in a radiocommunication system 100. The RN 120 may transmit data received from theeNodeB 110 to the UE 132 located in an RN area and transmit datareceived from the UE 132 located in the RN area to the eNodeB 110. Inaddition, the RN 120 may expand a high data rate area, improvecommunication quality in a cell edge, and support provision ofcommunication in a building or in an area other than a base stationservice area. In FIG. 1, the UE 131 (hereinafter, referred to as amacro-UE or M-UE) which directly receives a service from the eNodeB andthe UE 132 (hereinafter, referred to as a relay-UE or R-UE) whichreceives a service from the RN 120 are shown.

A wireless link between the eNodeB and the RN is called a backhaul link.A link from the eNodeB to the RN is called a backhaul downlink and alink from the RN to the eNodeB is called a backhaul uplink. In addition,a wireless link between the RN and the UE is called an access link. Alink from the RN to the UE is called an access downlink and a link fromthe UE to the RN is called an access uplink.

SUMMARY OF THE INVENTION

In order for a relay node (RN) to forward communication between an eNB(or BS) and a user equipment (UE), it is necessary to properlydiscriminate between resources used for communication on a backhaul linkbetween the eNB and the UE and other resources used for communication onan access link between the UE and the RN. This is called resourcepartitioning. In the case of the resource partitioning, the backhaullink between the eNB and the RN may be configured different from awireless link between the eNB and the UE for use in the legacy systemnot including the RN. Therefore, assuming that a conventional powerallocation scheme or a conventional channel estimation scheme is appliedto the backhaul link without any change, unexpected performancedeterioration or incorrect transmission/reception may occur. As such, itis necessary to develop and propose a new power allocation scheme, a newchannel estimation scheme, and the like for a backhaul link.

An object of the present invention devised to solve the problem lies inproviding a method for allocating power, a channel estimation method,and associated methods for configuring physical resources for a backhaullink between an eNB and an RN. Another object of the present inventiondevised to solve the problem lies in providing a channel estimationmethod for a Resource Block (RB) pair to which downlink (DL) schedulingcontrol information for the RN is transmitted in consideration ofprecoding and/or power allocation applied to DL resources when resourcesfor downlink from the eNB to the RN are allocated.

It will be appreciated by persons skilled in the art that the objectsthat can be achieved with the present invention are not limited to whathas been particularly described hereinabove and the above and otherobjects that the present invention can achieve will be more clearlyunderstood from the following detailed description taken in conjunctionwith the accompanying drawings.

The object of the present invention can be achieved by providing amethod for receiving a downlink signal at a relay node (RN) in awireless communication system, the method comprising receiving downlinkcontrol information by demodulating a Relay-Physical Downlink ControlChannel (R-PDCCH) of a first RB pair based on a downlink channelestimated by a Demodulation Reference Signal (DMRS) in the firstresource block (RB) pair; and receiving downlink data by demodulating aPhysical Downlink Shared Channel (PDSCH) of the one or more RB pairscontiguous to the first RB pair based on a downlink channel estimated bya DMRS in the one or more RB pairs, wherein, if the PDSCH is assigned tothe first RB pair, the downlink channel is estimated on the assumptionthat the same precoder is applied to one resource block (RB) bundleincluding the first RB pair and the one or more RB pairs.

In another aspect of the present invention, provided herein is a methodfor performing downlink transmission from a base station (BS) to a relaynode (RN) in a wireless communication system, the method comprisingtransmitting, in a first resource block (RB) pair, downlink controlinformation through a Relay-Physical Downlink Control Channel (R-PDCCH)and a Demodulation Reference Signal (DMRS) for estimating a downlinkchannel used for demodulating the R-PDCCH; and transmitting, in one ormore RB pairs contiguous to the first RB pair, downlink data through aPhysical Downlink Shared Channel (PDSCH) and a DMRS used for estimatinga downlink channel for demodulating the PDSCH, wherein, if the PDSCH isassigned to the first RB pair, the same precoder is applied to oneresource block (RB) bundle including the first RB pair and the one ormore RB pairs by the BS.

In still another aspect of the present invention, provided herein is arelay node for performing downlink reception comprising a firstreception module for receiving a downlink signal from a base station; afirst transmission module for transmitting an uplink signal to the basestation; a second reception module for receiving an uplink signal from auser equipment; a second transmission module for transmitting a downlinksignal to the user equipment; and a processor for controlling the relaynode including the first and second reception modules and the first andsecond transmission modules, wherein the processor is configured toreceive, through the first reception module, downlink controlinformation by demodulating a Relay-Physical Downlink Control Channel(R-PDCCH) of a first RB pair based on a downlink channel estimated by aDemodulation Reference Signal (DMRS) in the first resource block (RB)pair; and to receive, through the first reception module, the downlinkdata by demodulating a Physical Downlink Shared Channel (PDSCH) of theone or more RB pairs contiguous to the first RB pair based on a downlinkchannel estimated by a DMRS in the one or more RB pairs, wherein, if thePDSCH is assigned to the first RB pair, the downlink channel isestimated on the assumption that the same precoder is applied to oneresource block (RB) bundle including the first RB pair and the one ormore RB pairs.

In still another aspect of the present invention, provided herein is abase station for performing downlink transmission to a relay node in awireless communication system, the base station comprising a receptionmodule for receiving an uplink signal from the relay node; atransmission module for transmitting a downlink signal to the relaynode; and a processor for controlling the base station including thereception module and the transmission module, wherein the processor isconfigured to transmit, through the transmission module, in a firstresource block (RB) pair, downlink control information through aRelay-Physical Downlink Control Channel (R-PDCCH) and a DemodulationReference Signal (DMRS) for estimating a downlink channel used fordemodulating the R-PDCCH; and to transmit, through the transmissionmodule, in one or more RB pairs contiguous to the first RB pair,downlink data through a Physical Downlink Shared Channel (PDSCH) and aDMRS used for estimating a downlink channel for demodulating the PDSCH,wherein, if the PDSCH is assigned to the first RB pair, the sameprecoder is applied to one resource block (RB) bundle including thefirst RB pair and the one or more RB pairs by the base station.

The following matters are applicable to the embodiments of the presentinvention.

In case that the PDSCH is assigned to the first RB pair, the R-PDCCH isassigned to a first slot of the first RB pair, and the PDSCH is assignedto a second slot of the first RB pair.

In case that the PDSCH is not assigned to the first RB pair, thedownlink channel is estimated on the assumption that the same precoderis applied to one RB bundle including the one or more RB pairs otherthan the first RB pair. Further, in case that the PDSCH is not assignedto the first RB pair, the R-PDCCH is assigned to a first slot of thefirst RB pair, and an R-PDCCH transmitting uplink grant controlinformation or a null signal is transmitted to a second slot of thefirst RB pair.

The downlink channel is estimated using all DMRSs transmitted in the oneRB bundle.

The one RB bundle includes RB pairs transmitted in one subframe.

The one RB bundle including the first RB pair is applied to channelestimation for each of one or more downlink layers used for transmittingthe R-PDCCH.

The one RB bundle including the first RB pair is applied to downlinkchannel estimation for the case that a number of downlink layers assumedfor decoding R-PDCCH is three or more.

One RB pair includes two slots, and, if a DMRS for a specific antennaport is transmitted in one of the two slots of the one RB pair, the DMRSfor the specific antenna port is transmitted in the other one of the twoslots of the one RB pair.

Downlink grant control information is transmitted through the R-PDCCH.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

The embodiments of the present invention can provide a method forallocating power, a channel estimation method, and associated methodsfor establishing physical resources for a backhaul link between an eNBand an RN, such that power allocation and channel estimation for abackhaul link can be correctly and efficiently performed. In addition,when resources for DL from the eNB to the RN are allocated, the presentinvention can provide a channel estimation method for a Resource Block(RB) pair to which DL scheduling control information for the RN istransmitted in consideration of precoding and/or power allocationapplied to DL resources.

It is to be understood that the advantages that can be obtained by thepresent invention are not limited to the aforementioned advantages andother advantages which are not mentioned will be apparent from thefollowing description to those of an ordinary skill in the art to whichthe present invention pertains.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1 is a diagram illustrating a wireless communication systemincluding an eNB, an RN and a UE.

FIG. 2 is a diagram exemplarily shows a radio frame structure for use ina 3rd Generation Partnership Project Long Term Evolution (3GPP LTE)system.

FIG. 3 is a diagram exemplarily shows a resource grid of a DL slot.

FIG. 4 is a diagram shows downlink (DL) subframe structure.

FIG. 5 is a diagram shows an uplink (UL) subframe structure.

FIG. 6, including view (a) and view (b), is a diagram illustrating theconfiguration of a wireless communication system having multipleantennas.

FIG. 7, including view (a) and view (b), is a diagram shows a DLreference signal pattern defined in the 3GPP LTE system.

FIG. 8, including view (a) and view (b), is a diagram shows aUE-specific reference signal pattern defined in the 3GPP LTE-A system.

FIG. 9 is a diagram illustrating reference signal transmission in anuplink subframe.

FIG. 10 is a diagram exemplarily shows a transceiver of a FrequencyDivision Duplex-mode relay node.

FIG. 11 is a diagram exemplarily shows relay node resource partitioning.

FIG. 12 is a diagram illustrating that more power is allocated to afirst slot in a resource block (RB) pair to which a Relay-PhysicalDownlink Control Channel (R-PDCCH) is transmitted.

FIG. 13 is a diagram shows examples in which different DMRS(Demodulation Reference Signal) transmission powers are configured in afirst slot and a second slot within a resource block (RB) pair.

FIG. 14 is a diagram exemplarily shows a power allocation of a firstslot and a second slot of one RB pair.

FIG. 15 is a diagram exemplarily shows the number of RB pairs to whichR-PDCCH is assigned.

FIGS. 16 to 19 show examples in which a virtual resource block (RB)bundle is configured when some RB pair(s) of one RB bundle transmitR-PDCCH.

FIGS. 20 and 21 show examples in which a DMRS pattern dependent upon arank is considered.

FIG. 22 shows examples in which a scrambling ID used in one RB bundle isconsidered.

FIG. 23 is a flowchart illustrating an exemplary DL channel estimationoperation of a relay node (RN).

FIG. 24 is a block diagram illustrating an eNB and a relay node (RN)according to embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following embodiments are proposed by combining constituentcomponents and characteristics of the present invention according to apredetermined format. The individual constituent components orcharacteristics should be considered to be optional factors on thecondition that there is no additional remark. If required, theindividual constituent components or characteristics may not be combinedwith other components or characteristics. Also, some constituentcomponents and/or characteristics may be combined to implement theembodiments of the present invention. The order of operations to bedisclosed in the embodiments of the present invention may be changed toanother. Some components or characteristics of any embodiment may alsobe included in other embodiments, or may be replaced with those of theother embodiments as necessary.

The embodiments of the present invention are disclosed on the basis of adata communication relationship between a base station and a terminal.In this case, the base station is used as a terminal node of a networkvia which the base station can directly communicate with the terminal.Specific operations to be conducted by the base station in the presentinvention may also be conducted by an upper node of the base station asnecessary.

In other words, it will be obvious to those skilled in the art thatvarious operations for enabling the base station to communicate with theterminal in a network composed of several network nodes including thebase station will be conducted by the base station or other networknodes other than the base station. The term “Base Station (BS)” may bereplaced with a fixed station, Node-B, eNode-B (eNB), or an access pointas necessary. The term “relay” may be replaced with a Relay Node (RN) ora Relay Station (RS). The term “terminal” may also be replaced with aUser Equipment (UE), a Mobile Station (MS), a Mobile Subscriber Station(MSS) or a Subscriber Station (SS) as necessary.

It should be noted that specific terms disclosed in the presentinvention are proposed for the convenience of description and betterunderstanding of the present invention, and the use of these specificterms may be changed to another format within the technical scope of thepresent invention.

In some instances, well-known structures and devices are omitted inorder to avoid obscuring the concepts of the present invention and theimportant functions of the structures and devices are shown in blockdiagram form. The same reference numbers will be used throughout thedrawings to refer to the same or like parts.

Exemplary embodiments of the present invention are supported by standarddocuments disclosed for at least one of wireless access systemsincluding an Institute of Electrical and Electronics Engineers (IEEE)802 system, a 3^(rd) Generation Project Partnership (3GPP) system, a3GPP Long Term Evolution (LTE) system, and a 3GPP2 system. Inparticular, the steps or parts, which are not described to clearlyreveal the technical idea of the present invention, in the embodimentsof the present invention may be supported by the above documents. Allterminology used herein may be supported by at least one of theabove-mentioned documents.

The following embodiments of the present invention can be applied to avariety of wireless access technologies, for example, CDMA (CodeDivision Multiple Access), FDMA (Frequency Division Multiple Access),TDMA (Time Division Multiple Access), OFDMA (Orthogonal FrequencyDivision Multiple Access), SC-FDMA (Single Carrier Frequency DivisionMultiple Access), and the like. The CDMA may be embodied with wireless(or radio) technology such as UTRA (Universal Terrestrial Radio Access)or CDMA2000. The TDMA may be embodied with wireless (or radio)technology such as GSM (Global System for Mobile communications)/GPRS(General Packet Radio Service)/EDGE (Enhanced Data Rates for GSMEvolution). The OFDMA may be embodied with wireless (or radio)technology such as Institute of Electrical and Electronics Engineers(IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, and E-UTRA(Evolved UTRA). The UTRA is a part of the UMTS (Universal MobileTelecommunications System). The 3GPP (3rd Generation PartnershipProject) LTE (long term evolution) is a part of the E-UMTS (EvolvedUMTS), which uses E-UTRA. The 3GPP LTE employs the OFDMA in downlink andemploys the SC-FDMA in uplink. The LTE-Advanced (LTE-A) is an evolvedversion of the 3GPP LTE. WiMAX can be explained by an IEEE 802.16e(WirelessMAN-OFDMA Reference System) and an advanced IEEE 802.16m(WirelessMAN-OFDMA Advanced System). For clarity, the followingdescription focuses on the 3GPP LTE and 3GPP LTE-A system. However,technical features of the present invention are not limited thereto.

FIG. 2 is a diagram showing the structure of a radio frame used in a3^(rd) Generation Partnership Project Long Term Evolution (3GPP LTE)system. One radio frame includes 10 subframes, and one subframe includestwo slots in a time domain. A time for transmitting one subframe isdefined in a Transmission Time Interval (TTI). For example, one subframemay have a length of 1 ms and one slot may have a length of 0.5 ms. Oneslot may include a plurality of OFDM symbols in a time domain. Since the3GPP LTE system uses an OFDMA scheme in downlink, the OFDM symbolindicates one symbol period. One symbol may be called a SC-FDMA symbolor a symbol period in uplink. A Resource Block (RB) is a resourceallocation unit and includes a plurality of consecutive carriers in oneslot. The above structure of the radio frame is only exemplary.Accordingly, the number of subframes included in one radio frame, thenumber of slots included in one subframe or the number of OFDM symbolsincluded in one slot may be changed in various manners.

FIG. 3 is a diagram showing a resource grid in a downlink slot. Althoughone downlink slot includes seven OFDM symbols in a time domain and oneRB includes 12 subcarriers in a frequency domain in the figure, thepresent invention is not limited thereto. For example, in case of anormal Cyclic Prefix (CP), one slot includes 7 OFDM symbols. However, incase of an extended CP, one slot includes 6 OFDM symbols. Each elementon the resource grid is referred to as a resource element. One RBincludes 12×7 resource elements. The number N^(DL) of RBs included inthe downlink slot is determined based on a downlink transmissionbandwidth. The structure of the uplink slot may be equal to thestructure of the downlink slot.

FIG. 4 is a diagram showing the structure of a downlink subframe. Amaximum of three OFDM symbols of a front portion of a first slot withinone subframe corresponds to a control region to which a control channelis allocated. The remaining OFDM symbols correspond to a data region towhich a Physical Downlink Shared Channel (PDSCH) is allocated. Examplesof the downlink control channels used in the 3GPP LTE system include,for example, a Physical Control Format Indicator Channel (PCFICH), aPhysical Downlink Control Channel (PDCCH), a Physical Hybrid automaticrepeat request Indicator Channel (PHICH), etc. The PCFICH is transmittedat a first OFDM symbol of a subframe, and includes information about thenumber of OFDM symbols used to transmit the control channel in thesubframe. The PHICH includes a HARQ ACK/NACK signal as a response ofuplink transmission. The control information transmitted through thePDCCH is referred to as Downlink Control Information (DCI). The DCIincludes uplink or downlink scheduling information or an uplink transmitpower control command for a certain UE group. The PDCCH may includeresource allocation and transmission format of a Downlink Shared Channel(DL-SCH), resource allocation information of an Uplink Shared Channel(UL-SCH), paging information of a Paging Channel (PCH), systeminformation on the DL-SCH, resource allocation of an higher layercontrol message such as a Random Access Response (RAR) transmitted onthe PDSCH, a set of transmit power control commands for an individualUEs in a certain UE group, transmit power control information,activation of Voice over IP (VoIP), etc. A plurality of PDCCHs may betransmitted within the control region. The UE may monitor the pluralityof PDCCHs. The PDCCH is transmitted on an aggregation of one or severalconsecutive control channel elements (CCEs). The CCE is a logicalallocation unit used to provide the PDCCHs at a coding rate based on thestate of a radio channel. The CCE corresponds to a plurality of resourceelement groups. The format of the PDCCH and the number of available bitsare determined based on a correlation between the number of CCEs and thecoding rate provided by the CCEs. The number of CCEs used for PDCCHtransmission is referred to as a CCE aggregation level. In addition, theCCR aggregation level is a CCE unit for searching for PDCCH. The size ofthe CCE aggregation level is defined as the number of contiguous CCEs.For example, the CCE aggregation level may be 1, 2, 4 or 8.

The base station determines a PDCCH format according to a DCI to betransmitted to the UE, and attaches a Cyclic Redundancy Check (CRC) tocontrol information. The CRC is masked with a Radio Network TemporaryIdentifier (RNTI) according to an owner or usage of the PDCCH. If thePDCCH is for a specific UE, a cell-RNTI (C-RNTI) of the UE may be maskedto the CRC. Alternatively, if the PDCCH is for a paging message, apaging indicator identifier (P-RNTI) may be masked to the CRC. If thePDCCH is for system information (more specifically, a system informationblock (SIB)), a system information identifier and a system informationRNTI (SI-RNTI) may be masked to the CRC. To indicate a random accessresponse that is a response for transmission of a random access preambleof the UE, a random access-RNTI (RA-RNTI) may be masked to the CRC.

FIG. 5 is a diagram showing the structure of an uplink frame. The uplinksubframe may be divided into a control region and a data region in afrequency domain. A Physical Uplink Control Channel (PUCCH) includinguplink control information is allocated to the control region. APhysical uplink Shared Channel (PUSCH) including user data is allocatedto the data region. In order to maintain single carrier property, one UEdoes not simultaneously transmit the PUCCH and the PUSCH. The PUCCH forone UE is allocated to a RB pair in a subframe. RBs belonging to the RBpair occupy different subcarriers with respect to two slots. Thus, theRB pair allocated to the PUCCH is “frequency-hopped” at a slot boundary.

Modeling of Multi-Input Multi-Output (MIMO) System

FIG. 6, including view (a) and view (b), is a diagram showing theconfiguration of a radio communication system having multiple antennas.

As shown in FIG. 6(a), if the number of transmission antennas isincreased to N_(T) and the number of reception antennas is increased toN_(R), a theoretical channel transmission capacity is increased inproportion to the number of antennas, unlike the case where a pluralityof antennas is used in only a transmitter or a receiver. Accordingly, itis possible to improve a transfer rate and to remarkably improvefrequency efficiency. As the channel transmission capacity is increased,the transfer rate may be theoretically increased by a product of amaximum transfer rate R₀ upon using a single antenna and a rate increaseratio R_(i).R _(i)=min(N _(T) ,N _(R))  [Equation 1]

For example, in an MIMO system using four transmission antennas and fourreception antennas, it is possible to theoretically acquire a transferrate which is four times that of a single antenna system. After theincrease in the theoretical capacity of the MIMO system was proved inthe mid-1990s, various technologies of substantially improving a datatransfer rate have been actively developed up to now. In addition,several technologies are already applied to the various radiocommunication standards such as the third-generation mobilecommunication and the next-generation wireless local area network (LAN).

According to the researches into the MIMO antenna up to now, variousresearches such as researches into information theory related to thecomputation of the communication capacity of a MIMO antenna in variouschannel environments and multiple access environments, researches intothe model and the measurement of the radio channels of the MIMO system,and researches into space-time signal processing technologies ofimproving transmission reliability and transmission rate have beenactively conducted.

The communication method of the MIMO system will be described in moredetail using mathematical modeling. In the above system, it is assumedthat N_(T) transmission antennas and N_(R) reception antennas arepresent.

In transmitted signals, if the N_(T) transmission antennas are present,the number of pieces of maximally transmittable information is N_(T).The transmitted information may be expressed as follows.s=└s ₁ ,s ₂ , . . . ,s _(N) _(T) ┘^(T)  [Equation 2]

The transmitted information s₁, s₂, . . . , s_(N) _(T) may havedifferent transmit powers. If the respective transmit powers are P₁, P₂,. . . , P_(N) _(T) , the transmitted information with adjusted powersmay be expressed as follows.ŝ=[ŝ ₁ ,ŝ ₂ , . . . ,ŝ _(N) _(T) ]^(T) =[P ₁ s ₁ ,P ₂ s ₂ , . . . ,P_(N) _(T) s _(N) _(T) ]^(T)  [Equation 3]

In addition, ŝ may be expressed using a diagonal matrix P of thetransmit powers as follows.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\{0\;} & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Consider that the N_(T) actually transmitted signals x₁, x₂, . . . ,x_(N) _(T) are configured by applying a weight matrix W to theinformation vector ŝ with the adjusted transmit powers. The weightmatrix W serves to appropriately distribute the transmitted informationto each antenna according to a transport channel state, etc. x₁, x₂, . .. , x_(N) _(T) may be expressed by using the vector X as follows.

$\begin{matrix}\begin{matrix}{x = \begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{bmatrix}} \\{= {\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1N_{T}} \\w_{21} & w_{22} & \ldots & w_{2N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 1} & w_{i\; 2} & \ldots & w_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \ldots & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\\vdots \\{\hat{s}}_{j} \\\vdots \\{\hat{s}}_{N_{T}}\end{bmatrix}}} \\{= {W\hat{s}}} \\{= {WPs}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

where, w_(ij) denotes a weight between an i-th transmission antenna andj-th information. W is also called a precoding matrix.

In received signals, if the N_(R) reception antennas are present,respective received signals y₁, y₂, . . . , y_(N) _(R) of the antennasare expressed as follows.y=[y ₁ ,y ₂ , . . . ,y _(N) _(R) ]^(T)  [Equation 6]

If channels are modeled in the MIMO radio communication system, thechannels may be distinguished according to transmission/receptionantenna indexes. A channel from the transmission antenna j to thereception antenna i is denoted by h_(ij). In h_(ij), it is noted thatthe indexes of the reception antennas precede the indexes of thetransmission antennas in view of the order of indexes.

FIG. 6(b) is a diagram showing channels from the N_(T) transmissionantennas to the reception antenna i. The channels may be combined andexpressed in the form of a vector and a matrix. In FIG. 6(b), thechannels from the N_(T) transmission antennas to the reception antenna imay be expressed as follows.h _(i) ^(T) =[h _(i1) ,h _(i2) , . . . ,h _(iN) _(T])   [Equation 7]

Accordingly, all the channels from the N_(T) transmission antennas tothe N_(R) reception antennas may be expressed as follows.

$\begin{matrix}{H = {\begin{bmatrix}h_{1}^{T} \\h_{2}^{T} \\\vdots \\h_{i}^{T} \\\vdots \\h_{N_{R}}^{T}\end{bmatrix} = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

An Additive White Gaussian Noise (AWGN) is added to the actual channelsafter a channel matrix H. The AWGN n₁, n₂, . . . , n_(N) _(R) added tothe N_(T) transmission antennas may be expressed as follows.n=[n ₁ ,n ₂ , . . . ,n _(N) _(R) ]^(T)  [Equation 9]

Through the above-described mathematical modeling, the received signalsmay be expressed as follows.

$\begin{matrix}\begin{matrix}{y = \begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{i} \\\vdots \\y_{N_{R}}\end{bmatrix}} \\{= {{\begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{j} \\\vdots \\x_{N_{T}}\end{bmatrix}} + \begin{bmatrix}n_{1} \\n_{2} \\\vdots \\n_{i} \\\vdots \\x_{N_{R}}\end{bmatrix}}} \\{= {{Hx} + n}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$

The number of rows and columns of the channel matrix H indicating thechannel state is determined by the number of transmission and receptionantennas. The number of rows of the channel matrix H is equal to thenumber N_(R) of reception antennas and the number of columns thereof isequal to the number N_(T) of transmission antennas. That is, the channelmatrix H is an N_(R)×N_(T) matrix.

The rank of the matrix is defined by the smaller of the number of rowsor columns, which is independent from each other. Accordingly, the rankof the matrix is not greater than the number of rows or columns. Therank rank(H) of the channel matrix H is restricted as follows.rank(H)≦min(N _(T) ,N _(R))  [Equation 11]

When the matrix is subjected to Eigen value decomposition, the rank maybe defined by the number of Eigen values excluding 0. Similarly, whenthe matrix is subjected to singular value decomposition, the rank may bedefined by the number of singular values excluding 0. Accordingly, thephysical meaning of the rank in the channel matrix may be a maximumnumber of different transmittable information in a given channel.

Reference Signal (RS)

In a radio communication system, since packets are transmitted through aradio channel, a signal may be distorted during transmission. In orderto enable a reception side to correctly receive the distorted signal,distortion of the received signal should be corrected using channelinformation. In order to detect the channel information, a method oftransmitting a signal, of which both the transmission side and thereception side are aware, and detecting channel information using adistortion degree when the signal is received through a channel ismainly used. The above signal is referred to as a pilot signal or areference signal (RS).

When transmitting and receiving data using multiple antennas, thechannel states between the transmission antennas and the receptionantennas should be detected in order to correctly receive the signal.Accordingly, each transmission antenna has an individual RS.

A downlink RS includes a Common RS (CRS) shared among all UEs in a celland a Dedicated RS (DRS) for only a specific-UE. It is possible toprovide information for channel estimation and demodulation using suchRSs.

The reception side (UE) estimates the channel state from the CRS andfeeds back an indicator associated with channel quality, such as aChannel Quality Indicator (CQI), a Precoding Matrix Index (PMI) and/or aRank Indicator (RI), to the transmission side (eNodeB). The CRS may bealso called a cell-specific RS. Alternatively, an RS associated with thefeedback of Channel State Information (CSI) such as CQI/PMI/RI may beseparately defined as a CSI-RS.

The DRS may be transmitted through REs if data demodulation on a PDSCHis necessary. The UE may receive the presence/absence of the DRS from ahigher layer and receive information indicating that the DRS is validonly when the PDSCH is mapped. The DRS may be also called a UE-specificRS or a Demodulation RS (DMRS).

FIG. 7, including view (a) and view (b), is a diagram showing a patternof CRSs and DRSs mapped on a downlink RB pair defined in the existing3GPP LTE system (e.g., Release-8). The downlink RB pair as a mappingunit of the RSs may be expressed in units of one subframe on a timedomain×12 subcarriers on a frequency domain. That is, on the time axis,one RB pair has a length of 14 OFDM symbols in case of the normal CP(FIG. 7(a)) and has a length of 12 OFDM symbols in case of the extendedCP (FIG. 7(b)).

FIG. 7 shows the locations of the RSs on the RB pair in the system inwhich the eNodeB supports four transmission antennas. In FIG. 7,Resource Elements (REs) denoted by “0”, “1”, “2” and “3” indicate thelocations of the CRSs of the antenna port indexes 0, 1, 2 and 3,respectively. In FIG. 7, the RE denoted by “D” indicates the location ofthe DRS.

Hereinafter, the CRS will be described in detail.

The CRS is used to estimate the channel of a physical antenna and isdistributed over the entire band as an RS which is able to be commonlyreceived by all UEs located within a cell. The CRS may be used for CSIacquisition and data demodulation.

The CRS is defined in various formats according to the antennaconfiguration of the transmission side (eNodeB). The 3GPP LTE (e.g.,Release-8) system supports various antenna configurations, and adownlink signal transmission side (eNodeB) has three antennaconfigurations such as a single antenna, two transmission antennas andfour transmission antennas. If the eNodeB performs single-antennatransmission, RSs for a single antenna port are arranged. If the eNodeBperforms two-antenna transmission, RSs for two antenna ports arearranged using a Time Division Multiplexing (TDM) and/or FrequencyDivision Multiplexing (FDM) scheme. That is, the RSs for the two antennaports are arranged in different time resources and/or differentfrequency resources so as to be distinguished from each other. Inaddition, if the eNodeB performs four-antenna transmission, RSs for fourantenna ports are arranged using the TDM/FDM scheme. The channelinformation estimated by the downlink signal reception side (UE) throughthe CRSs may be used to demodulate data transmitted using a transmissionscheme such as single antenna transmission, transmit diversity,closed-loop spatial multiplexing, open-loop spatial multiplexing, orMulti-User MIMO (MU-MIMO).

If multiple antennas are supported, when RSs are transmitted from acertain antenna port, the RSs are transmitted at the locations of theREs specified according to the RS pattern and any signal is nottransmitted at the locations of the REs specified for another antennaport.

The rule of mapping the CRSs to the RBs is defined by Equation 12.

$\begin{matrix}\begin{matrix}{k = {{6m} + {\left( {v + v_{shift}} \right){mod}\; 6}}} \\{l = \left\{ \begin{matrix}{0,{N_{symb}^{DL} - 3}} & {{{if}\mspace{14mu} p} \in \left\{ {0,1} \right\}} \\1 & {{{if}\mspace{14mu} p} \in \left\{ {2,3} \right\}}\end{matrix} \right.} \\{{m = 0},1,\ldots\mspace{14mu},{{2 \cdot N_{RB}^{DL}} - 1}} \\{m^{\prime} = {m + N_{RB}^{\max,{DL}} - N_{RB}^{DL}}} \\{v = \left\{ \begin{matrix}0 & {{{if}\mspace{14mu} p} = {{0\mspace{14mu}{and}\mspace{14mu} l} = 0}} \\3 & {{{if}\mspace{14mu} p} = {{0\mspace{14mu}{and}\mspace{14mu} l} \neq 0}} \\3 & {{{if}\mspace{14mu} p} = {{1\mspace{14mu}{and}\mspace{14mu} l} = 0}} \\0 & {{{if}\mspace{14mu} p} = {{1\mspace{14mu}{and}\mspace{14mu} l} \neq 0}} \\{3\left( {n_{s}{mod}\; 2} \right)} & {{{if}\mspace{14mu} p} = 2} \\{3 + {3\left( {n_{s}{mod}\; 2} \right)}} & {{{if}\mspace{14mu} p} = 3}\end{matrix} \right.} \\{v_{shift} = {N_{ID}^{cell}{mod}\; 6}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack\end{matrix}$

In Equation 12, k denotes a subcarrier index, l denotes a symbol index,and p denotes an antenna port index. N_(symb) ^(DL) denotes the numberof OFDM symbols of one downlink slot, N_(RB) ^(DL) denotes the number ofRBs allocated to the downlink, n_(s) denotes a slot index, N_(ID)^(cell) denotes a cell ID and mod indicates a modulo operation. Thelocation of the RS in the frequency domain depends on a value V_(shift).Since the value V_(shif) depends on the cell ID, the location of the RShas a frequency shift value which varies according to the cell.

In detail, in order to increase channel estimation performance throughthe CRSs, the locations of the CRSs in the frequency domain may beshifted so as to be changed according to the cells. For example, if theRSs are located at an interval of three subcarriers, the RSs arearranged on 3k-th subcarriers in one cell and arranged on (3k+1)-thsubcarriers in the other cell. In view of one antenna port, the RSs arearranged at an interval of 6 REs (that is, interval of 6 subcarriers) inthe frequency domain and are separated from REs, on which RSs allocatedto another antenna port are arranged, by 3 REs in the frequency domain.

In addition, power boosting is applied to the CRSs. The power boostingindicates that the RSs are transmitted using higher power by bringing(stealing) the powers of the REs except for the REs allocated for theRSs among the REs of one OFDM symbol.

In the time domain, the RSs are arranged from a symbol index (l=0) ofeach slot as a starting point at a constant interval. The time intervalis differently defined according to the CP length. The RSs are locatedon symbol indexes 0 and 4 of the slot in case of the normal CP and arelocated on symbol indexes 0 and 3 of the slot in case of the extendedCP. Only RSs for a maximum of two antenna ports are defined in one OFDMsymbol. Accordingly, upon four-transmission antenna transmission, theRSs for the antenna ports 0 and 1 are located on the symbol indexes 0and 4 (the symbol indexes 0 and 3 in case of the extended CP) of theslot and the RSs for the antenna ports 2 and 3 are located on the symbolindex 1 of the slot. The frequency locations of the RSs for the antennaports 2 and 3 in the frequency domain are exchanged with each other in asecond slot.

In order to support spectrum efficiency higher than that of the existing3GPP LTE (e.g., Release-8) system, a system (e.g., an LTE-A system)having the extended antenna configuration may be designed. The extendedantenna configuration may have, for example, eight transmissionantennas. In the system having the extended antenna configuration, UEswhich operate in the existing antenna configuration needs to besupported, that is, backward compatibility needs to be supported.Accordingly, it is necessary to support a RS pattern according to theexisting antenna configuration and to design a new RS pattern for anadditional antenna configuration. If CRSs for the new antenna ports areadded to the system having the existing antenna configuration, RSoverhead is rapidly increased and thus data transfer rate is reduced. Inconsideration of these problems, in an LTE-A (Advanced) system which isan evolution version of the 3GPP LTE system, separate RSs (CSI-RSs) formeasuring the CSI for the new antenna ports may be used.

Hereinafter, the DRS will be described in detail.

The DRS (or the UE-specific RS) is used to demodulate data. A precodingweight used for a specific UE upon multi-antenna transmission is alsoused in an RS without change so as to estimate an equivalent channel, inwhich a transfer channel and the precoding weight transmitted from eachtransmission antenna are combined, when the UE receives the RSs.

The existing 3GPP LTE system (e.g., Release-8) supportsfour-transmission antenna transmission as a maximum and the DRS for Rank1 beamforming is defined. The DRS for Rank 1 beamforming is also denotedby the RS for the antenna port index 5. The rule of the DRS mapped onthe RBs is defined by Equations 13 and 14. Equation 13 is for the normalCP and Equation 14 is for the extended CP.

$\begin{matrix}\begin{matrix}{k = {{\left( k^{\prime} \right){mod}\; N_{sc}^{RB}} + {N_{sc}^{RB} \cdot n_{PRB}}}} \\{k^{\prime} = \left\{ \begin{matrix}{{4m^{\prime}} + v_{shift}} & {{{if}\mspace{14mu} l} \in \left\{ {2,3} \right\}} \\{{4m^{\prime}} + {\left( {2 + v_{shift}} \right){mod}\; 4}} & {{{if}\mspace{14mu} l} \in \left\{ {5,6} \right\}}\end{matrix} \right.} \\{l = \left\{ \begin{matrix}3 & {l^{\prime} = 0} \\6 & {l^{\prime} = 1} \\2 & {l^{\prime} = 2} \\5 & {l^{\prime} = 3}\end{matrix} \right.} \\{l^{\prime} = \left\{ \begin{matrix}{0,1} & {{{if}\mspace{14mu} n_{s}{mod}\; 2} = 0} \\{2,3} & {{{if}\mspace{14mu} n_{s}{mod}\; 2} = 1}\end{matrix} \right.} \\{{m^{\prime} = 0},1,\ldots\mspace{14mu},{{3N_{RB}^{PDSCH}} - 1}} \\{v_{shift} = {N_{ID}^{cell}{mod}\; 3}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 13} \right\rbrack \\\begin{matrix}{k = {{\left( k^{\prime} \right){mod}\; N_{sc}^{RB}} + {N_{sc}^{RB} \cdot n_{PRB}}}} \\{k^{\prime} = \left\{ \begin{matrix}{{3m^{\prime}} + v_{shift}} & {{{if}\mspace{14mu} l} = 4} \\{{3m^{\prime}} + {\left( {2 + v_{shift}} \right){mod}\; 3}} & {{{if}\mspace{14mu} l} = 1}\end{matrix} \right.} \\{l = \left\{ \begin{matrix}4 & {l^{\prime} \in \left\{ {0,2} \right\}} \\1 & {l^{\prime} = 1}\end{matrix} \right.} \\{l^{\prime} = \left\{ \begin{matrix}0 & {{{if}\mspace{14mu} n_{s}{mod}\; 2} = 0} \\{1,2} & {{{if}\mspace{14mu} n_{s}{mod}\; 2} = 1}\end{matrix} \right.} \\{{m^{\prime} = 0},1,\ldots\mspace{14mu},{{4N_{RB}^{PDSCH}} - 1}} \\{v_{shift} = {N_{ID}^{cell}{mod}\; 3}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 14} \right\rbrack\end{matrix}$

In Equations 13 and 14, k denotes a subcarrier index, l denotes a symbolindex, and p denotes an antenna port index. N_(SC) ^(RB) denotes theresource block size in the frequency domain and is expressed by thenumber of subcarriers. n_(PRB) denotes a physical resource block number.N_(RB) ^(PDSCH) denotes the bandwidth of the RB of the PDSCHtransmission. n_(s) denotes a slot index, and N_(ID) ^(cell) denotes acell ID. mod indicates a modulo operation. The location of the RS in thefrequency domain depends on a value V_(shift). Since the value V_(shif)depends on the cell ID, the location of the RS has a frequency shiftvalue which varies according to the cell.

In the LTE-A system which is the evolution version of the 3GPP LTEsystem, high-order MIMO, multi-cell transmission, evolved MU-MIMO or thelike is considered. In order to support efficient RS management and adeveloped transmission scheme, DMRS-based data demodulation isconsidered. That is, separately from the DMRS (antenna port index 5) forRank 1 beamforming defined in the existing 3GPP LTE (e.g., Release-8)system, DMRSs for two or more layers may be defined in order to supportdata transmission through the added antenna. DMRS may be configured tobe transmitted only in a resource block and layer in which DLtransmission is scheduled by an eNB.

An exemplary DMRS pattern newly introduced to LTE-A (LTE Release-10 orthe next LTE Release) will hereinafter be described with reference toFIG. 8, including view (a) and view (b). The overhead of a DMRS newlyintroduced to support an extended antenna configuration (e.g., a maximumof 8 Tx antennas) may vary. In case of a lower rank (e.g., either Rank 1or Rank 2), DMRS may be arranged on 12 REs in one RB pair (See FIG.8(a)). In case of a higher rank (e.g., any one of Ranks 3 to 8), DMRSmay be present in 24 REs of one RB pair (See FIG. 8(b)). When DMRSs arearranged on RB, DMRS for each layer may be multiplexed and arranged onthe RB. Time Division Multiplexing (TDM) indicates that DMRSs for two ormore layers are allocated to different time resources (e.g., OFDMsymbols). Frequency Division Multiplexing (FDM) indicates that DMRSs fortwo or more layers are allocated to different frequency resources (e.g.,subcarriers). Code Division Multiplexing (CDM) indicates that DMRSs fortwo or more layers arranged on the same radio resources are multiplexedusing an orthogonal sequence (or orthogonal covering) either betweenOFDM symbols for the corresponding RS resource elements or betweenfrequency subcarriers.

The DMRS pattern shown in FIG. 8 is configured in a mixed form of CDMand FDM. For example, CDM group 1 may be mapped to ports 1, 2, 5 and 6,and CDM group 2 may be mapped to ports 3, 4, 7 and 8. According to suchmapping relationship, the number of REs occupied by DMRSs per channelrank is changed. In accordance with a CDM+FDM scheme, 12 REs/RBs/portsare used for DMRS for Rank 1 or Rank 2 (See FIG. 8(a)), 24 REs/RBs/portsare used for DMRS for any one of Ranks 3 to 8 (See FIG. 8(b)). Althoughthe above-mentioned description has assumed that antenna ports relatedto DMRS transmission used for PDSCH demodulation are antenna ports 1 to8, the scope of the present invention is not limited thereto. Forexample, in order to discriminate between a conventional CRS-relatedantenna port (antenna ports 0 to 3) and a conventional DRS-relatedantenna port (antenna port 5), antenna ports related to DMRStransmission may be represented by antenna ports 7 to 14.

Cooperative Multi-Point (CoMP)

According to the improved system performance requirements of the 3GPPLTE-A system, CoMP transmission/reception technology (may be referred toas co-MIMO, collaborative MIMO or network MIMO) is proposed. The CoMPtechnology can increase the performance of the UE located on a cell edgeand increase average sector throughput.

In general, in a multi-cell environment in which a frequency reusefactor is 1, the performance of the UE located on the cell edge andaverage sector throughput may be reduced due to Inter-Cell Interference(ICI). In order to reduce the ICI, in the existing LTE system, a methodof enabling the UE located on the cell edge to have appropriatethroughput and performance using a simple passive method such asFractional Frequency Reuse (FFR) through the UE-specific power controlin the environment restricted by interference is applied. However,rather than decreasing the use of frequency resources per cell, it ispreferable that the ICI is reduced or the UE reuses the ICI as a desiredsignal. In order to accomplish the above object, a CoMP transmissionscheme may be applied.

The CoMP scheme applicable to the downlink may be largely classifiedinto a Joint Processing (JP) scheme and a CoordinatedScheduling/Beamforming (CS/CB) scheme.

In the JP scheme, each point (eNodeB) of a CoMP unit may use data. TheCoMP unit refers to a set of eNodeBs used in the CoMP scheme. The JPscheme may be classified into a joint transmission scheme and a dynamiccell selection scheme.

The joint transmission scheme refers to a scheme for transmitting aPDSCH from a plurality of points (a part or the whole of the CoMP unit).That is, data transmitted to a single UE may be simultaneouslytransmitted from a plurality of transmission points. According to thejoint transmission scheme, it is possible to coherently ornon-coherently improve the quality of the received signals and toactively eliminate interference with another UE.

The dynamic cell selection scheme refers to a scheme for transmitting aPDSCH from one point (of the CoMP unit). That is, data transmitted to asingle UE at a specific time is transmitted from one point and the otherpoints in the cooperative unit at that time do not transmit data to theUE. The point for transmitting the data to the UE may be dynamicallyselected.

According to the CS/CB scheme, the CoMP units may cooperatively performbeamforming of data transmission to a single UE. Although only a servingcell transmits the data, user scheduling/beamforming may be determinedby the coordination of the cells of the CoMP unit.

In uplink, coordinated multi-point reception refers to reception of asignal transmitted by coordination of a plurality of geographicallyseparated points. The CoMP scheme applicable to the uplink may beclassified into Joint Reception (JR) and CoordinatedScheduling/Beamforming (CS/CB).

The JR scheme indicates that a plurality of reception points receives asignal transmitted through a PUSCH, the CS/CB scheme indicates that onlyone point receives a PUSCH, and user scheduling/beamforming isdetermined by the coordination of the cells of the CoMP unit.

Sounding RS (SRS)

An SRS is used for enabling an eNodeB to measure channel quality so asto perform frequency-selective scheduling on the uplink and is notassociated with uplink data and/or control information transmission.However, the present invention is not limited thereto and the SRS may beused for improved power control or supporting of various start-upfunctions of UEs which are not recently scheduled. Examples of thestart-up functions may include, for example, initial Modulation andCoding Scheme (MCS), initial power control for data transmission, timingadvance, and frequency-semi-selective scheduling (scheduling forselectively allocating frequency resources in a first slot of a subframeand pseudo-randomly hopping to another frequency in a second slot).

In addition, the SRS may be used for downlink channel qualitymeasurement on the assumption that the radio channel is reciprocalbetween the uplink and downlink. This assumption is particularly validin a Time Division Duplex (TDD) system in which the same frequency bandis shared between the uplink and the downlink and is divided in the timedomain.

The subframe through which the SRS is transmitted by a certain UE withinthe cell is indicated by cell-specific broadcast signaling 4-bitcell-specific “srsSubframeConfiguration” parameter indicates 15 possibleconfigurations of the subframe through which the SRS can be transmittedwithin each radio frame. By such configurations, it is possible toprovide adjustment flexibility of SRS overhead according to a networkarrangement scenario. The remaining one (sixteenth) configuration of theparameters indicates the switch-off of the SRS transmission within thecell and is suitable for a serving cell for serving high-rate UEs.

As shown in FIG. 9, the SRS is always transmitted on a last SC-FDMAsymbol of the configured subframe. Accordingly, the SRS and aDemodulation RS (DMRS) are located on different SC-FDMA symbols. PUSCHdata transmission is not allowed on the SC-FDMA symbol specified for SRStransmission and thus sounding overhead does not approximately exceed 7%even when it is highest (that is, even when SRS transmission symbols arepresent in all subframes).

Each SRS symbol is generated by the basic sequence (random sequence orZadoff-Ch (ZC)-based sequence set) with respect to a given time unit andfrequency band, and all UEs within the cell use the same basic sequence.At this time, the SRS transmission of the plurality of UEs within thecell in the same time unit and the same frequency band is orthogonallydistinguished by different cyclic shifts of the base sequence allocatedto the plurality of UEs. The SRS sequences of different cells can bedistinguished by allocating different basic sequences to respectivecells, but the orthogonality between the different basic sequences isnot guaranteed.

Relay Node (RN)

The RN may be considered for, for example, enlargement of high data ratecoverage, improvement of group mobility, temporary network deployment,improvement of cell edge throughput and/or provision of network coverageto a new area.

Referring to FIG. 1 again, the RN 120 forwards data transmitted orreceived between the eNodeB 110 and the UE 131, two different links(backhaul link and access link) are applied to the respective carrierfrequency bands having different attributes. The eNodeB 110 may includea donor cell. The RN 120 is wirelessly connected to a radio accessnetwork through the donor cell 110.

The backhaul link between the eNodeB 110 and the RN 120 may berepresented by a backhaul downlink if downlink frequency bands ordownlink subframe resources are used, and may be represented by abackhaul uplink if uplink frequency bands or uplink subframe resourcesare used. Here, the frequency band is resource allocated in a FrequencyDivision Duplex (FDD) mode and the subframe is resource allocated in aTime Division Duplex (TDD) mode. Similarly, the access link between theRN 120 and the UE(s) 131 may be represented by an access downlink ifdownlink frequency bands or downlink subframe resources are used, andmay be represented by an access uplink if uplink frequency bands oruplink subframe resources are used. FIG. 1 shows the setting of thebackhaul uplink/downlink and the access uplink/downlink of the FDD-modeRN.

The eNodeB must have functions such as uplink reception and downlinktransmission and the UE must have functions such as uplink transmissionand downlink reception. The RN must have all functions such as backhauluplink transmission to the eNodeB, access uplink reception from the UE,the backhaul downlink reception from the eNodeB and access downlinktransmission to the UE.

FIG. 10 is a diagram showing an example of implementing transmission andreception functions of a FDD-mode RN. The reception function of the RNwill now be conceptually described. A downlink signal received from theeNodeB is forwarded to a Fast Fourier Transform (FFT) module 1012through a duplexer 1011 and is subjected to an OFDMA baseband receptionprocess 1013. An uplink signal received from the UE is forwarded to aFFT module 1022 through a duplexer 1021 and is subjected to a DiscreteFourier Transform-spread-OFDMA (DFT-s-OFDMA) baseband reception process1023. The process of receiving the downlink signal from the eNodeB andthe process of receiving the uplink signal from the UE may besimultaneously performed. The transmission function of the RN will nowbe described. The uplink signal transmitted to the eNodeB is transmittedthrough a DFT-s-OFDMA baseband transmission process 1033, an Inverse FFT(IFFT) module 1032 and a duplexer 1031. The downlink signal transmittedto the UE is transmitted through an OFDM baseband transmission process1043, an IFFT module 1042 and a duplexer 1041. The process oftransmitting the uplink signal to the eNodeB and the process oftransmitting the downlink signal to the UE may be simultaneouslyperformed. In addition, the duplexers shown as functioning in onedirection may be implemented by one bidirectional duplexer. For example,the duplexer 1011 and the duplexer 1031 may be implemented by onebidirectional duplexer and the duplexer 1021 and the duplexer 1041 maybe implemented by one bidirectional duplexer. The bidirectional duplexermay branch into the IFFT module associated with the transmission andreception on a specific carrier frequency band and the baseband processmodule line.

In association with the use of the band (or the spectrum) of the RN, thecase where the backhaul link operates in the same frequency band as theaccess link is referred to as “in-band” and the case where the backhaullink and the access link operate in different frequency bands isreferred to as “out-band”. In both the in-band case and the out-bandcase, a UE which operates according to the existing LTE system (e.g.,Release-8), hereinafter, referred to as a legacy UE, must be able to beconnected to the donor cell.

The RN may be classified into a transparent RN or a non-transparent RNdepending on whether or not the UE recognizes the RN. The term“transparent” indicates that the UE cannot recognize whethercommunication with the network is performed through the RN and the term“non-transparent” indicates that the UE recognizes whether communicationwith the network is performed through the RN.

In association with the control of the RN, the RN may be classified intoa RN configured as a part of the donor cell or a RN for controlling thecell.

The RN configured as the part of the donor cell may have a RN ID, butdoes not have its cell identity. When at least a part of Radio ResourceManagement (RRM) of the RN is controlled by the eNodeB to which thedonor cell belongs (even when the remaining parts of the RRM are locatedon the RN), the RN is configured as the part of the donor cell.Preferably, such an RN can support a legacy UE. For example, examples ofsuch an RN include various types of relays such as smart repeaters,decode-and-forward relays, L2 (second layer) relays and Type-2 relays.

In the RN for controlling the cell, the RN controls one or severalcells, unique physical layer cell identities are provided to the cellscontrolled by the RN, and the same RRM mechanism may be used. From theviewpoint of the UE, there is no difference between access to the cellcontrolled by the RN and access to the cell controlled by a generaleNodeB. Preferably, the cell controlled by such an RN may support alegacy UE. For example, examples of such an RN include self-backhaulingrelays, L3 (third layer) relays, Type-1 relays and Type-1a relays.

The Type-1 relay is an in-band relay for controlling a plurality ofcells, which appears to be different from the donor cell, from theviewpoint of the UE. In addition, the plurality of cells has respectivephysical cell IDs (defined in the LTE Release-8) and the RN may transmitits synchronization channel, RSs, etc. In a single-cell operation, theUE may directly receive scheduling information and HARQ feedback fromthe RN and transmit its control channel (Scheduling Request (SR), CQI,ACK/NACK, etc.) to the RN. In addition, a legacy UE (a UE which operatesaccording to the LTE Release-8 system) regards the Type-1 relay as alegacy eNodeB (an eNodeB which operates according to the LTE Release-8system). That is, the Type-1 relay has backward compatibility. The UEswhich operates according to the LTE-A system regard the Type-1 relay asan eNodeB different from the legacy eNodeB, thereby achievingperformance improvement.

The Type-1a relay has the same characteristics as the above-describedType-1 relay except that it operates as an out-band relay. The Type-1arelay may be configured so as to minimize or eliminate an influence ofthe operation thereof on an L1 (first layer) operation.

The Type-2 relay is an in-band relay and does not have a separatephysical cell ID. Thus, a new cell is not established. The Type-2 relayis transparent to the legacy UE and the legacy UE does not recognize thepresence of the Type-2 relay. The Type-2 relay can transmit a PDSCH, butdoes not transmit at least a CRS and a PDCCH.

In order to enable the RN to operate as the in-band relay, someresources in a time-frequency space must be reserved for the backhaullink so as not to be used for the access link. This is called resourcepartitioning.

The general principle of the resource partitioning in the RN will now bedescribed. The backhaul downlink and the access downlink may bemultiplexed on one carrier frequency using a Time Division Multiplexing(TDM) scheme (that is, only one of the backhaul downlink or the accessdownlink is activated in a specific time). Similarly, the backhauluplink and the access uplink may be multiplexed on one carrier frequencyusing the TDM scheme (that is, only one of the backhaul uplink or theaccess uplink is activated in a specific time).

The multiplexing of the backhaul link using a FDD scheme indicates thatbackhaul downlink transmission is performed in a downlink frequency bandand the backhaul uplink transmission is performed in an uplink frequencyband. The multiplexing of the backhaul link using the TDD schemeindicates that the backhaul downlink transmission is performed in adownlink subframe of the eNodeB and the RN and the backhaul uplinktransmission is performed in an uplink subframe of the eNodeB and theRN.

In the in-band relay, for example, if the backhaul downlink receptionfrom the eNodeB and the access downlink transmission to the UE aresimultaneously performed in a predetermined frequency band, the signaltransmitted from the transmitter of the RN may be received by thereceiver of the RN and thus signal interference or RF jamming may occurin the RF front end of the RN. Similarly, if the access uplink receptionfrom the UE and the backhaul uplink transmission to the eNodeB aresimultaneously performed in a predetermined frequency band, signalinterference may occur in the RF front end of the RN. Accordingly, it isdifficult to implement the simultaneous transmission and reception inone frequency band at the RN unless the received signal and thetransmitted signal are sufficiently separated (for example, unless thetransmission antennas and the reception antennas are sufficientlyseparated from each other (for example, on the ground or under theground) in terms of geographical positions).

As a method for solving the signal interference, the RN operates so asnot to transmit a signal to the UE while a signal is received from thedonor cell. That is, a gap may be generated in the transmission from theRN to the UE and any transmission from the RN to the UE (including thelegacy UE) may not be performed. Such a gap may be set by configuring aMulticast Broadcast Single Frequency Network (MBSFN) subframe (see FIG.11). In FIG. 11, a first subframe 1110 is a normal subframe, in which adownlink (that is, access downlink) control signal and data istransmitted from the RN to the UE, and a second subframe 1120 is anMBSFN subframe, in which a control signal is transmitted from the RN tothe UE in a control region 1121 of the downlink subframe, but any signalis not transmitted from the RN to the UE in the remaining region 1122 ofthe downlink subframe. Since the legacy UE expects the transmission ofthe PDCCH in all downlink subframes (that is, the RN needs to enable thelegacy UEs within its own area to receive the PDCCH in every subframe soas to perform a measurement function), for the correct operation of thelegacy UEs, it is necessary to transmit the PDCCH in all the downlinksubframes. Accordingly, even on the subframe (the second subframe 1120))set for the transmission of the downlink (that is, the backhauldownlink) from the eNodeB to the RN, the RN needs to transmit the accessdownlink in first N (N=1, 2 or 3) OFDM symbol intervals of the subframe,without receiving the backhaul downlink. Since the PDCCH is transmittedfrom the RN to the UE in the control region 1121 of the second subframe,it is possible to provide backward compatibility to the legacy UE servedby the RN. While any signal is not transmitted from the RN to the UE inthe remaining region 1122 of the second subframe, the RN may receive thesignal transmitted from the eNodeB. Accordingly, the resourcepartitioning disables the in-band RN to simultaneously perform theaccess downlink transmission and the backhaul downlink reception.

The second subframe 1122 using the MBSFN subframe will now be describedin detail. The control region 1121 of the second subframe may be a RNnon-hearing interval. The RN non-hearing interval refers to an intervalin which the RN does not receive a backhaul downlink signal andtransmits an access downlink signal. This interval may be set to 1, 2 or3 OFDM lengths as described above. The RN performs the access downlinktransmission to the UE in the RN non-hearing interval 1121 and performsthe backhaul downlink reception from the eNodeB in the remaining region1122. At this time, since the RN cannot simultaneously perform thetransmission and reception in the same frequency band, it takes acertain length of time to switch the RN from the transmission mode tothe reception mode. Accordingly, it is necessary to set a guard time(GT) to switch the RN from the transmission mode to the reception modein a first portion of the backhaul downlink reception region 1122.Similarly, even when the RN receives the backhaul downlink from theeNodeB and transmits the access downlink to the UE, a guard time (GT) toswitch the RN from the reception mode to the transmission mode may beset. The length of the guard time may be set to values of the timedomain, for example, values of k (k≧1) time samples Ts or one or moreOFDM symbol lengths. Alternatively, if the backhaul downlink subframesof the RN are consecutively set or according to a predetermined subframetiming alignment relationship, the guard time of a last portion of thesubframes may not be defined or set. Such a guard time may be definedonly in the frequency domain set for the transmission of the backhauldownlink subframe, in order to maintain backward compatibility (thelegacy UE cannot be supported if the guard time is set in the accessdownlink interval). The RN can receive a PDCCH and a PDSCH from theeNodeB in the backhaul downlink reception interval 1122 except for theguard time. Such PDCCH and the PDSCH are physical channels dedicated forRN and thus may be represented by an R-PDCCH (Relay-PDCCH) and anR-PDSCH (Relay-PDSCH). Alternatively, R-PDSCH may be simply referred toas PDSCH. In accordance with the present invention, a physical downlinkshared channel (PDSCH) for a relay node (RN) may be represented by PDSCHonly for convenience of description and better understanding of thepresent invention.

Backhaul Link Power Allocation

A method for allocating transmission (Tx) power in backhaul linktransmission between eNB and RN according to various embodiments of thepresent invention will hereinafter be described in detail. Backhaul Txpower is flexibly allocated such that channel estimation and decoding ofan R-PDCCH as a channel for transmitting various control signals fromthe eNB to the RN can be more correctly and effectively performed.

Power Allocation in Units of RB Pair

Power allocation for use in a backhaul link according to the presentinvention will hereinafter be described on the basis of one RB pair. Inthis case, one RB pair may be defined as the length of one subframe(corresponding to 2 slots or 14 OFDM symbols for use in a normal CP) ona time domain×the size of one RB (composed of 12 subcarriers) on afrequency domain. In addition, an RB pair may correspond to a PhysicalResource Block (RPB) pair.

In accordance with one embodiment of the present invention, higher powermay be allocated to an RB pair to which R-PDCCH is transmitted ascompared to other regions. In more detail, the aforementioned higherpower allocation may also be considered as power boosting of the RB pairin which R-PDCCH is transmitted. Power boosting indicates that power isderived from REs other than some REs to which power boosting is appliedso that data or information can be transmitted with higher power at thecorresponding RE. Through the power boosting for the RB pair related toR-PDCCH transmission, the RN can more correctly decode important controlinformation.

The aforementioned power boosting may be applied only to a transmissionsignal of the R-PDCCH, may be applied only to a reference signal (RS)for demodulating the R-PDCCH, or may be applied to both the transmissionsignal and the reference signal (RS) of R-PDCCH. If DMRS is used toperform R-PDCCH demodulation, a specific RN-dedicated RS (or anRN-specific RS) is used so that the use of power boosting only in the RBpair in which the R-PDCCH is transmitted may be considered to exhibitefficient performance.

On the other hand, the eNB and the RN may transmit/receive, via higherlayer, signals requesting or indicating whether to perform powerboosting for the R-PDCCH in consideration of a channel state of abackhaul link and how much power boosting will be applied if powerboosting is applied.

If the RN performs channel estimation using the DMRS, channel estimationfor the R-PDCCH may also be used to demodulate a data signal transmittedthrough a PDSCH in the same RB pair or different RB pairs. In this case,power boosting is not applied to a data signal through the PDSCH, sothat decoding throughput of the data signal may be deteriorated when thechannel estimated by the power-boosted DMRS is applied to the datasignal without change. Accordingly, if the reference signal (RS) for theR-PDCCH is power-boosted, appropriate interpolation with DMRS of thePDSCH is performed by the RN in consideration of the power boostingdegree so that the data signal can be correctly decoded.

Power Allocation on Basis of Slot

The above-mentioned embodiment of the present invention has describedbackhaul link power allocation on the basis of one RB pair. In addition,according to one example of the present invention, a first slot and asecond slot contained in one RB pair may be assigned different Txpowers.

For example, higher Tx power may be assigned to the first slot of one RBpair as compared to the second slot, or higher Tx power may be assignedto the second slot as compared to the first slot. Alternatively,predetermined power may be assigned to a DMRS of the first slot of oneRB pair, and no power (i.e., a zero-power signal or null signal) may beassigned to a DMRS of the second slot.

In order to determine which slot will be power-boosted within one RBpair, the operation of RN for receiving control information and datathrough a backhaul DL link is considered. In order for the RN to receivedata for the RN over a PDSCH, the RN must receive a DL grant includinginformation such as DL resource allocation information from the eNB overthe R-PDCCH, and recognize control information (i.e., position of PDSCHfor the RN, MCS level, etc.) indicated by the DL grant, so that it canreceive and decode the PDSCH. In addition, the RN may inform the eNB ofthe PDSCH decoding result upon transmission of ACK/NACK. In other words,PDSCH decoding may be performed only after reception of the DL grantover the R-PDCCH. Considering the above, if the DL grant is transmittedfrom the second slot of a certain subframe, PDSCH decoding can beperformed only after one subframe has been completely received,resulting in reduction in a time available for PDSCH decoding by the RN.If transmission of the DL grant through the R-PDCCH is limited to afirst slot of the backhaul DL subframe, the RN can apply a timecorresponding to the second slot to perform the PDSCH decoding. As such,the RN can have more time for PDSCH decoding, resulting in reduction inRN implementation costs. For example, a high-speed decoder (i.e., ahigh-priced decoder) need not be used. As described above, if theR-PDCCH is limited to be positioned only in the first slot of one RBpair, it is preferable that higher Tx power be assigned to the firstslot than the second slot.

FIG. 12 is a conceptual diagram illustrating that higher power isallocated to a first slot in an RB pair in which R-PDCCH is transmitted.Referring to FIG. 12, a part denoted by PDCCH in the first slot is apart in which the RN does not receive a backhaul DL signal (seenon-hearing interval 1121 of FIG. 11), and the part may be excluded froman object to which backhaul link power boosting is applied. As detailedexamples for power boosting at the first slot of one RB pair, powerboosting can be applied to one or both of an R-PDCCH signal and areference signal (RS).

Alternatively, even when no signal (or zero-power signal) is applied tothe second slot of one RB pair, the RS may be transmitted with constantpower within the second slot, so as to prevent deterioration of overallchannel estimation performance caused when the RS is not transmitted insome slots under the condition that channel estimation is simultaneouslyperformed in a bundle composed of the one RB pair and some contiguous RBpairs. As a result, neither data nor control signal is transmitted inthe second slot, but the RS (DMRS and/or CRS) may be transmitted in thesecond slot. For example, when a DMRS for a specific antenna port (e.g.,at least one of antenna ports 7 to 14) is transmitted in one (e.g., afirst slot) of two slots contained in one certain RB pair, a DMRS forthe same antenna port as in the DMRS of the one slot (e.g., the firstslot) may also be configured to transmitted in the other one (e.g., asecond slot) of the two slots of the corresponding RB pair. In thiscase, RS transmission power of one of the two slots contained in one RBpair may be identical to that of the other slot.

As shown in FIG. 12, a UL grant or a PDSCH may be transmitted or nosignal may be transmitted in the second slot of the RB pair in which aDL grant is transmitted, and associated examples thereof willhereinafter be described in detail.

UL Grant Transmitted in Second Slot

UL grant may be transmitted in a second slot of one RB pair of abackhaul downlink. The UL grant includes control information about ULtransmission resource allocation of the RN, and may be provided from theeNB to the RN through the R-PDCCH.

The UL grant transmitted in the second slot may be limited to the sameRN as an RN acting as a destination of DL transmission by the DL grantin the first slot. Such limitation may be useful especially for backhaullink transmission employing a DMRS because the same precoding can beapplied to the first and second slots. In more detail, precoding isapplied to the DMRS and the DMRS is an RN-specific RS, theaforementioned limitation is useful especially for backhaul linktransmission employing DMRS. On the other hand, if a CRS is applied tobackhaul DL transmission, the aforementioned limitation may not beapplied.

Provided that DMRS is used for backhaul link transmission and the ULgrant and the DL grant are transmitted for the same RN, the RN thatreceives one RB pair including a first slot to which power boosting isapplied, may operate in such a manner that the UL grant received in thesecond slot is decoded only using the DMRS of the first slot. Providedthat the DMRS received in the first slot is sufficiently power-boostedfor DL grant decoding of the corresponding RN, the UL grant of thesecond slot can be decoded using only the DMRS of the first slot. Inthis manner, if the RN decodes the UL grant of the second slot onlyusing the DMRS of the first slot, the eNB may set DMRS power of thesecond slot to zero (0), or may utilize the corresponding power fortransmission of other signals as necessary.

If the DMRS power of the second slot is lower than the DMRS power of thefirst slot and is higher than zero (0), the RN may use DMRSs of thefirst and second slots so as to more correctly perform channelestimation. If the RN performs channel estimation using DMRSs of thefirst and second slots, a predetermined power boosting level for thefirst slot (or a difference in DMRS transmission power between the firstslot and the second slot) may be considered. The RN may decode the ULgrant of the second slot using channel estimation in which powerboosting of the first slot is considered. For the above-mentionedoperation, the RN needs to recognize DMRS transmission power in eachslot. If the transmission power of the DMRS is not equal to zero (0),the corresponding power offset can be transmitted from the eNB to the RNthrough RRC signaling or L1/L2 signaling.

In accordance with the above-mentioned description, total transmissionpower required by the eNB may be saved as much as the transmission powerof the second slot of one RB pair is set low. The saved transmissionpower can be adapted to increase transmission power of a signaltransmitted through another RB pair within the same time interval(subframe). For example, the saved transmission power may be used toperform boosting of transmission power (DMRS transmission power and/orR-PDCCH signal transmission power) of the UL grant transmitted in thesecond slot of another RB pair. For example, under the condition thatthe DL grant for a specific RN is not present but the UL grant for thespecific RN is present, if the UL grant is transmitted to the secondslot, the transmission power of the first slot for the corresponding RNis saved so that the saved transmission power can be used to performpower boosting of the DL grant of another RN as described above.Alternatively, in association with the UL grant of the second slot forthe corresponding RN, power boosting may be applied to another RN whosesecond slot has no DRMS (or the UL grant is not present in the secondslot of the other RN) using the saved transmission power.

FIG. 13 shows a variety of examples in which DMRS transmission power isdifferently configured in a first slot and a second slot in associationwith two RNs configured to receive signals in different RB pairs (i.e.,RB pair 1 and RB pair 2). Differently from the example of FIG. 12, FIG.13 does not show a PDCCH region unrelated to power allocation betweenthe eNB and the RN. Referring to FIG. 13, DMRS transmission power may beboosted only in the first slot of the RB pair 1 for use in the RN 1, andDMRS transmission power may be set to a low value in the second slot ofthe RB pair 1. Due to the aforementioned power allocation in the RB pair1, low DMRS transmission power is assigned to the first slot of the RBpair 2 for use in the RN 2, and DMRS transmission power may be boostedonly in the second slot. That is, the transmission power saved in the RBpair 2 of the first slot may be used to boost DMRS power of the RB pair1, and the transmission power saved in the RB pair 1 of the second slotmay be used to boost DMRS power of the RB pair 2. Through theabove-mentioned power allocation, effective power sharing can beimplemented.

In order to more effectively apply the above-mentioned power sharing,the position of a DMRS used for decoding the R-PDCCH may be variablyconfigured according to individual situations.

First of all, the RN may attempt to decode the DL grant of the firstslot using the DMRS of the first slot. For example, when the RN decodesthe DL grant of the first slot using the DMRS of the first slot, if theDL grant of the first slot is decoded, the RN may decode the UL grant ofthe second slot using the DMRS of the first slot. Alternatively,provided that the RN fails to decode the DL grant of the first slotusing the DMRS of the first slot, the RN may decode the UL grant of thesecond slot using the DMRS of the second slot.

Alternatively, in order to implement more simplified operations, whendecoding the UL grant of the second slot, the RN may be predefined toalways use the DMRS of the first slot, may be predefined to always usethe DMRS of the second slot, or may be predefined to always use allDMRSs of the first and second slots.

PDSCH Transmitted in Second Slot

PDSCH transmitted in the second slot may be limited only to the same RNas a RN related to the DL grant of the first slot. This limitation maybe useful for backhaul link transmission employing a DMRS because thesame precoding can be applied to the first slot and the second slot. Inmore detail, precoding is applied to the DMRS and the DMRS is anRN-specific RS, so that the aforementioned limitation is useful. On theother hand, if a CRS is used for backhaul DL transmission, theaforementioned limitation need not be applied.

Referring back to FIG. 12, under the condition that power boosting isapplied to the DL grant, in order for the RN to correctly decode a PDSCHindicated by the corresponding DL grant, it is necessary for the RN toproperly reflect a difference in DMRS power between the first slot andthe second slot when performing channel estimation. For this operation,the eNB may inform the corresponding RN of the difference in DMRS powerbetween the first slot and the second slot of the RB pair in which theDL grant is transmitted. Information about such power difference may betransmitted to the RN using either a physical layer signal through anR-PDSCH or a higher layer signal. Alternatively, in order to easilyimplement the channel estimation operation, the embodiment of thepresent invention may include that transmission powers of DMRSs of thefirst and second slots of a certain RB pair are all boosted.

No Signal Transmitted in Second Slot

If it is assumed that no signal is transmitted in the second slot of theRB pair in which the DL grant is transmitted in the first slot, DMRStransmission power of the second slot may be set to zero (0). In thiscase, the RN may not apply the DMRS of the corresponding region tochannel estimation for another signal (e.g., PDSCH), because wrongchannel estimation may occur due to low transmission power of thecorresponding region and a difference in transmission power. As aresult, if the RN does not detect a signal in the second slot of the RBpair in which the DL grant is transmitted in the first slot, the RNassumes that the transmission power of a DMRS in the second slot of thecorresponding RB pair is zero (0), such that channel estimation or thelike can be performed on the above-mentioned assumption.

Backhaul Link Channel Estimation

A channel estimation method and a precoding method for a backhaul linkbetween the eNB and the RN according to embodiments of the presentinvention will hereinafter be described in detail. According to theembodiments of the present invention, different channel estimationmethods may be used according to whether a backhaul link control channel(e.g., R-PDCCH) is included in backhaul link resources. According to oneembodiment of the present invention, the RN that performs channelestimation for demodulating DL data using the DMRS may apply differentchannel estimation methods and different RB bundling methods to one RBpair in which an R-PDCCH is transmitted and the other RB pair in whichno R-PDCCH is transmitted. As a result, R-PDCCH and PDSCH can beeffectively multiplexed on backhaul DL resources.

In general, in order to increase channel estimation performance usingthe DMRS, channel estimation may be performed in units of one RB bundlecomposed of a certain number of contiguous RB pairs. In this case, thesame precoding and/or the same power allocation are/is applied to one RBbundle. Therefore, the receiver may simultaneously perform channelestimation using all the DMRSs of one RB bundle. For example, a channelobtained by averaging channels estimated through all the DMRSs of one RBbundle may be used as a channel for demodulation for all the RB pairs ofthe corresponding RB bundle. However, provided that the RB pair in whichthe R-PDCCH is transmitted is present, the above-mentioned channelestimation method in units of an RB bundle may be inappropriate, and adetailed description of a channel estimation method applied to the RBpair in which the R-PDCCH is transmitted will be given below.

Channel Estimation Operation in RS Pair in which R-PDCCH is Transmitted

A channel estimation operation of the RB pair in which R-PDCCH istransmitted will hereinafter be described in detail.

FIG. 14 shows exemplary power allocation for use in each of the firstslot and the second slot within one RB pair. In the RB pair 1 and the RBpair 2 shown in FIG. 14, a specific part denoted by PDCCH in the firstslot is a part in which the RN does not receive a backhaul DL signal(see non-hearing interval 1121 of FIG. 11), so that the PDCCH part isunrelated to the backhaul link channel estimation operation of thepresent invention.

The RB pair 1 shown in FIG. 14 exemplarily illustrates how powerboosting is applied to a first slot in which the DL grant is transmittedover the R-PDCCH, The RB pair 2 shown in FIG. 14 exemplarily illustratesthat no power boosting is applied when data is transmitted over a PDSCHin each of the first and second slots, and constant transmission poweris allocated to the first slot and the second slot.

For example, as can be seen from the RB pair 1 of FIG. 14, if powerboosting is applied to the first slot in which the DL grant istransmitted over the R-PDCCH, transmission power different from a DMRSof another RB pair (e.g., RB pair 2 of FIG. 14) is allocated to the DMRSof the RB pair 1. Therefore, if it is assumed that the RB pair 1 towhich power boosting is applied and the RB pair 2 to which no powerboosting is applied are combined and channel estimation is thenperformed on the combination of the RB pair 1 and the RB pair 2, channelestimation performance may be deteriorated or an actual channel statemay not be reflected in the channel estimation result. In other words,if one or more RB pairs contained in a certain RB bundle are used totransmit the R-PDCCH (thus power boosting is applied to some RB pairs towhich the R-PDCCH is transmitted), it is improper to perform channelestimation using the same method as in a normal RB bundle.

In order to solve the above-mentioned problem and perform the correctchannel estimation operation, when decoding the R-PDCCH irrespective ofapplication of the RB bundle, the embodiment of the present inventioncan perform channel estimation on the basis of RB(s) in which theR-PDCCH is transmitted.

When decoding the R-PDCCH, the channel estimation operation on the basisof RB(s) in which the R-PDCCH is transmitted may be limited to aspecific case in which an aggregation level of the R-PDCCH is equal toor less than a predetermined aggregation level. The aggregation level ofthe R-PDCCH may correspond to the number of CCEs used for R-PDCCHtransmission. For example, if the R-PDCCH aggregation level is set to 2or higher or is equal to or less than a specific value (for example, theaggregation level is set to 2 or is set to 2 or 4), it is assumed thatthe same precoding and/or the same power allocation are/is applied toRBs (a plurality of contiguous PRBs in a frequency domain) used forR-PDCCH transmission irrespective of the RB bundling definition, suchthat channel estimation can be performed in the corresponding RBs basedon the above assumption.

Alternatively, one R-PDCCH (DL grant or UL grant) may be transmittedover a plurality of RB pairs according to the amount of resources usedfor R-PDCCH transmission. In this case, it is assumed that the sameprecoding and/or the same power allocation are/is applied to theplurality of RB pairs over which the R-PDCCH is transmitted, such thatchannel estimation may be performed in the corresponding RBs based onthe above assumption.

FIG. 15 shows one case (RN1) in which R-PDCCH is transmitted over one RBand the other case (RN2) in which R-PDCCH is transmitted over two RBs.FIG. 15 exemplarily shows four RB pairs RB#1, RB#2, RB#3 and RB#4. Ascan be seen from FIG. 15, in a first slot of the RB#1, a DL grant istransmitted through the R-PDCCH for a first RN (RN1). In the RB#2, nosignal is transmitted. In the first slot of each of RB#3 and RB#4, theDL grant is transmitted through the R-PDCCH for a second RN (RN2).

As can be seen from the example of FIG. 15, when the first RN (RN1)decodes its own DL grant transmitted over the R-PDCCH of one RB pair,the RN1 can perform channel estimation only using one RB pair (i.e.,RB#1).

In addition, as shown in the example of FIG. 15, when the second RN(RN2) decodes its own DL grant transmitted over the R-PDCCH of two RBpairs, the RN2 can perform channel estimation simultaneously using twoRB pairs (RB#3 and RB#4) occupied by the R-PDCCH.

Alternatively, in order to more easily define the channel estimationoperation, although the RN2 transmits the R-PDCCH over a plurality of RBpairs (RB#3 and RB#4), the RN2 may perform independent channelestimation in each of the RB pairs (RB#3 and RN#4) irrespective of theabove R-PDCCH transmission. In more detail, in the case of channelestimation of the RB in which the R-PDCCH is transmitted, althoughseveral RBs are contained in the same RB bundle, the RN2 may not assumethat the same precoding and/or the same power allocation are/is appliedto the corresponding RBs in the RB bundle and then perform channelestimation based on the above assumption.

Channel Estimation Operation of RB Pair in which R-PDCCH is notTransmitted

A channel estimation operation in the RB pair to which no R-PDCCH istransmitted will hereinafter be described in detail.

The following description assumes that one RB bundle is comprised ofthree RB pairs. However, the scope of the present invention is notlimited thereto and can also be applied to other examples. That is, oneRB bundle may be configured with N RB pairs (where N≧2).

In accordance with one embodiment of the present invention, the R-PDCCHmay be configured to always occupy one or more RB bundles. That is,R-PDCCH is configured to be transmitted over one or more RB bundles sothat the R-PDCCH may not be transmitted only to some RB pairs of one RBbundle. Therefore, a channel estimation scheme for normal RB bundle canbe applied to the RB pairs in which the R-PDCCH is not transmittedwithout any change.

In another example, R-PDCCH may be transmitted in some RB pair(s)contained in one RB bundle, and R-PDCCH may not be transmitted in theremaining RB pair(s). Channel estimation method for this example of thepresent invention will be described in detail.

A detailed description of the embodiment in which a virtual RB bundlecomposed of one or more RB pairs in which no R-PDCCH is transmitted isconfigured in the RB bundle to which R-PDCCH is transmitted will begiven below.

FIG. 16 shows an exemplary case in which R-PDCCH is transmitted in someRB pairs of one RB bundle. For example, as shown in the resourceallocation scheme of FIG. 16, it can be assumed that R-PDCCH istransmitted only in one RB pair (RB#3) contained in one RB bundle (RBbundle #1) composed of three RB pairs (RB#3, RB#4 and RB#5). Under thiscondition, it may be assumed that the same precoding and/or the samepower allocation are/is applied only to the remaining RB pairs otherthan an RB pair in which R-PDCCH (or DL grant) is decoded within one RBbundle, such that channel estimation may then be performed based on theabove assumption. In other words, as can be seen from FIG. 16, three RBpairs consist one RB bundle, and one virtual RB bundle may be configuredwith the remaining RB pairs (RB#4 and RB#5) other than the RB pair(RB#3) that transmits R-PDCCH within the RB bundle (RB bundle #1)including R-PDCCH. Therefore, it is assumed that the same precodingand/or the same power allocation are applied on the basis of a virtualRB bundle, and the channel estimation operation may then be performedbased on this assumption. The channel estimation method for a normal RBbundle may be applied to the remaining RB bundles (RB bundle #0 and RBbundle #2) without any change.

One embodiment in which one or more RB pairs in which no R-PDCCH istransmitted within the RB bundle in which R-PDCCH is transmitted and acontiguous RB bundle constitute the virtual RB bundle will hereinafterbe described with reference to FIG. 17.

FIG. 17 shows an exemplary case in which the R-PDCCH is transmitted insome RB pairs of one RB bundle. For example, as shown in the resourceallocation of FIG. 17, it can be assumed that R-PDCCH is transmittedonly in one RB pair (RB#3) contained in one RB bundle (RB bundle #1)composed of three RB pairs (RB#3, RB#4 and RB#5). In this case, at leastone RB pair that does not transmit the R-PDCCH within the RB bundleincluding the R-PDCCH may be incorporated into a contiguous RB bundle.Under the resource allocation condition of FIG. 17, in the RB bundle (RBbundle #1) including the R-PDCCH, RB pairs (RB#4 and RB5) nottransmitting the R-PDCCH are incorporated into a contiguous RB bundle(e.g., RB bundle #2), so that a total of five RB pairs (RB#4 to RB#8)may constitute one virtual RB bundle. As a result, it is assumed thatthe same precoding and/or the same power allocation are/is applied inunits of a virtual RB bundle, and the channel estimation operation maythen be performed based on this assumption. The channel estimationmethod for a normal RB bundle may be applied to the remaining RB bundle(RB bundle #0) without change.

Another embodiment in which one or more RB pairs in which no R-PDCCH istransmitted within the RB bundle in which R-PDCCH is transmitted and acontiguous RB bundle constitute the virtual RB bundle will hereinafterbe described with reference to FIG. 18.

Differently from R-PDCCH transmission for use in the RB pair (RB#3) ofFIG. 17, FIG. 18 shows exemplary resource allocation in which theR-PDCCH is transmitted in another RB pair (RB#4). In this case, in theRB bundle (RB bundle #1) including R-PDCCH, RB pairs (RB#3 and RB#5) nottransmitting the R-PDCCH are contiguous with different RB bundles. Thatis, RB#3 is contiguous to the RB bundle #0, and RB#5 is contiguous tothe RB bundle #2. In this case, RB#4 is incorporated into the contiguousRB bundle (RB bundle #0) so that one virtual RB bundle is constituted.RB#5 is incorporated into the contiguous RB bundle (RB bundle #2) sothat another virtual RB bundle is constituted. Therefore, it is assumedthat the same precoding and/or the same power allocation are/is appliedin units of a virtual RB bundle, so that channel estimation can beperformed based on the above assumption.

The embodiment in which the RB bundle is reconfigured on the basis ofthe RB pair(s) in which R-PDCCH is transmitted according to the presentinvention will hereinafter be described with reference to FIG. 19.

Referring to exemplary resource allocation shown in FIG. 19, RB pairs(RB#0 to RB#2) constitute one RB bundle #0, RB pairs (RB#3 to RB#5)constitute one RB bundle #1, and RB pairs (RB#6 to RB#8) constitute oneRB bundle #2. For example, it is assumed that R-PDCCH is transmitted inRB#3. Therefore, in association with the RB bundle #1 in which some RBpairs transmit the R-PDCCH, it may be improper to perform channelestimation based on the assumption that the same precoding and/or thesame power allocation are/is applied to the RB bundle #1. In this case,one virtual RB bundle is composed of a predetermined number of RB pairscontiguous to both directions (low frequency direction and highfrequency direction in the example of FIG. 19) of the RB pair in whichR-PDCCH (or DL grant) is decoded and channel estimation may be performedusing the virtual RB bundle. In other words, it can be recognized thatRB bundles may be reconfigured on the basis of the RB pair in whichR-PDCCH (or DL grant) is decoded. For example, according to resourceallocation shown in FIG. 19, one virtual RB bundle may be composed ofthree RB pairs (RB#4, RB#5 and RB#6) in a high frequency direction onthe basis of RB#3 in which R-PDCCH (or DL grant) is decoded, and anothervirtual RB bundle may be composed of three subsequent RB pairs (RB#7,RB#8 and RB#9). On the other hand, one virtual RB bundle may be composedof three RB pairs (RB#0, RB#1 and RB#3) in a low frequency direction onthe basis of RB#3 in which R-PDCCH is transmitted. According to theaforementioned embodiment of the present invention, virtual RB bundlesthat are identical to or different from the configured RB bundles (RBbundle #0, RB bundle #1, RB bundle #2, etc.) according to the positionof the RB pair in which R-PDCCH is transmitted. RB bundles for all RBpairs are newly decided by repeating the process for constituting thevirtual RB bundle (i.e., the process for reconfiguration RB bundles),and it is assumed that the same precoding and/or the same powerallocation are/is applied to one reconfigured RB bundle, so that channelestimation can be performed based on this assumption.

Channel Estimation Application for Virtual RB Bundle

In embodiments of the present invention, according to variousreferences, channel estimation for the aforementioned virtual RB bundlemay be performed, or channel estimation may be performed on the basis ofa conventional RB bundle (or an RB bundle for PDSCH).

In accordance with the channel estimation scheme for the aforementionedvirtual RB bundle, in the case where R-PDCCH is allocated to a specificRB pair, an RB bundle is composed of the remaining RB pairs other thanthe specific RB pair (i.e., a virtual RB bundle is composed), andchannel estimation can be performed based on the assumption that thesame precoder is applied to the virtual RB bundle. In accordance withthe channel estimation scheme in units of the conventional RB bundle,the RN assumes that the same precoder is applied to the RB bundleincluding RB pairs (i.e., RB pairs in which R-PDCCH or PSDCH isallocated irrespective of channel categories) in which an RN signal isallocated, such that channel estimation is performed based on thisassumption. For this operation, in the case where a PDSCH is allocatedto a certain RB pair (irrespective of which channel is allocated to thisRB pair), the eNB may apply the same precoder to an RB bundle includingthis RB pair.

A variety of embodiments indicating whether channel estimation isapplied to a virtual RB bundle will hereinafter be described in detail.

FIGS. 20 and 21 illustrate DMRS patterns, each of which is dependentupon rank.

In FIGS. 20 and 21, the first three OFDM symbols (l=0, 1 and 2) show aduration in which the RN transmits a PDCCH to a Relay-UE and anotherduration in which the RN is switched from a transmission operation to areception operation (see non-hearing interval 1121 of FIG. 11). FIG. 20shows an exemplary DMRS pattern in case of Rank 1 or Rank 2, and FIG. 21shows an exemplary DMRS pattern in case of Rank 3 or higher.

As shown in FIG. 20, in the case of Rank 1, only a DMRS (i.e., DMRS port0) for a layer index 0 is transmitted. In the case of Rank 2, DMRSs(i.e., DMRS ports 0 and 1) for layer indexes 0 and 1 are transmitted.DMRSs for individual layers may be multiplexed at the same RE positionaccording to the CDM scheme. In the case of Rank 1 or Rank 2, DMRSoverhead is 12 REs within one RB pair. On the other hand, in the case ofRank 3 shown in FIG. 21, DMRSs (i.e., DMRS ports 0, 1, and 2) for layerindexes 0, 1 and 2 are transmitted. In the case of Rank 3 or higher,layer indexes 0, 1, 2, . . . , 7 (i.e., DMRS ports 0, 1, 2, . . . , 7)are transmitted. In the case of each of Ranks 3 to 8, DMRS overhead is24 REs within one RB pair. In other words, DMRS overhead for use in oneRB pair is 12 REs in case of Rank 1 and Rank 2, and is 24 REs in case ofRanks 3 to 8.

On the other hand, channel estimation based on DMRS may be performed foreach layer with the corresponding DMRS port. That is, individual layersmay correspond to different space resources, and individual spaceresources have different channel states, such that DMRS may be providedto individual layers (or individual antenna ports) so as to performchannel estimation of the corresponding space channel. For example,channel estimation using DMRS for the DMRS port 0 may be the channelestimation result of a channel transmitted on the corresponding layer 0.Although the above-mentioned example has described antenna port indexes0 to 7 for DMRS, antenna port indexes for DMRS may be represented byantenna port indexes 7 to 14 in such a manner that the above-mentionedantenna port indexes can be distinguished from conventional antennaports (e.g., antenna ports 0 to 3 for CRS) for other RSs.

In accordance with one embodiment of the present invention, a method forconstituting a virtual RB bundle according to various examples of thepresent invention may be applied only to channel estimation of a DMRSport of a specific rank or higher.

If a transmission rank of R-PDCCH is limited to Rank 1 or Rank 2, onlyDMRSs of a maximum of two ports (DMRS ports 0 and 1) need to betransmitted in an RB pair in which R-PDCCH (or DL grant) is transmitted,and signals of DMRS ports (DMRS ports 2 to 7) corresponding to Rankshigher than Rank 1 or Rank 2 need not be transmitted. For example, inthe case where data of Rank 3 or higher is not multiplexed in an RB pairin which R-PDCCH is transmitted, DMRS may be transmitted only in DMRSports 0 and 1 of the corresponding RB pair. For example, in a certain RBpair such as the DMRS pattern of FIG. 20, in the case where an R-PDCCH(or DL grant) limited to Rank 2 is transmitted in a first slot and aPDSCH less than Rank 2 is transmitted in a second slot (or in the casewhere an R-PDCCH limited to Rank 2 is transmitted in the second slot orno signal is transmitted in the second slot), only DMRSs through DMRSports 0 and 1 can be transmitted in the corresponding RB pair as shownin FIG. 20.

In this case, in the RB bundle including RB pairs in which R-PDCCHlimited to Rank 2 is transmitted, channel estimation for layers (i.e.,DMRS port 0 or 1) used in R-PDCCH transmission may be performed on thebasis of a conventional RB bundle (or an RB bundle for PDSCH). Forexample, in the case where R-PDCCH is transmitted in the RB pair (RB#3)as shown in FIG. 16, in relation to Rank 1 and Rank 2 (i.e., in relationto Layers 0 and 1), although an RB pair in which R-PDCCH is transmittedis present in the RB bundle, it is assumed that the same precodingand/or the same power allocation are/is applied to all RB pairs (RB#3,RB#4 and RB#5) of the RB bundle #1, such that channel estimation can beperformed based on this assumption. In other words, according to thepresent invention, in association with the RB bundle including RB pairsin which R-PDCCH is transmitted, channel estimation for the layer(s)used for R-PDCCH transmission may be performed on the basis of theconventional RB bundle (or the RB bundle for PDSCH), instead ofconstituting the virtual RB bundle shown in FIG. 16.

In addition, it is assumed that, in a certain RB pair of an RB bundleincluding RB pair(s) in which R-PDCCH limited to Rank 2 is transmitted,a PDSCH is transmitted with a transmission rank (e.g., Rank 3) higherthan the transmission rank of the R-PDCCH. In this case, in an RB pairin which the R-PDCCH limited to Rank 2 is transmitted, DMRS for Layer 0or 1 may be transmitted in the RB pair, but DMRSs for Layers 2 to 7 maynot be transmitted in the RB pair. Therefore, for the remaining layers(Layers 2, 3, . . . 7) other than Layers 0 and 1 in association withtransmission of Rank 3 or higher, it is preferable that the virtual RBbundles shown in one of FIGS. 16 to 19 are applied to the remaininglayers and channel estimation is then performed.

For example, in the case of resource allocation in which R-PDCCH istransmitted in the RB pair (RB#3) as shown in FIG. 16, channelestimation for the DMRS ports 0 and 1 may be performed on the assumptionthat the same precoding and/or the same power allocation are/is appliedto RB pairs (RB#3 to RB#5) (i.e., on the basis of a conventional RBbundle). On the other hand, channel estimation for DMRS ports 2 to 7 maybe performed on the assumption that the same precoding and/or the samepower allocation are/is applied only to a virtual RB bundle composed ofonly RB#4 and RB#5 other than RB#3. Alternatively, in order to performchannel estimation for DMRS ports 2 to 7, the virtual RB bundle may beconfigured in the same manner as in one of FIGS. 16 to 19.

On the other hand, according to the another examples of the presentinvention, application of the method for constituting a virtual RBbundle may be determined according to the number of DMRS ports assumedwhen R-PDCCH is decoded in the first slot.

For example, in the case where R-PDCCH is decoded on the assumption thata maximum of 2 DMRS ports are used in a first slot of a certain RB pairas shown in FIG. 20, DMRSs for layers 2 to 7 may not be transmitted inthe corresponding RB pair. In this case, the RB pair in which R-PDCCH(or DL grant) is transmitted is not incorporated into the RB bundle fora PDSCH, and a virtual RB bundle as shown in one of FIGS. 16 to 19 isconstituted such that channel estimation can be performed.

In the case where R-PDCCH is decoded in a first slot of a certain RBpair on the assumption of three or more DMRS ports as shown in FIG. 21,DMRSs for all layers can be transmitted in the corresponding RB pair. Inthis case, an RB pair in which R-PDCCH (or DL grant) is transmitted isincorporated into the RB bundle for PDSCH in such a manner that channelestimation can be performed in units of a conventional RB bundle.

In FIGS. 20 and 21, the number of DMRS ports transmitted in the secondslot may be changed according to a rank value of a signal transmitted inthe corresponding position. In case of PDSCH, the rank value may beindicated by the DL grant. In case of R-PDCCH, the rank value may bepredetermined or may be decided according to the number of DMRSs.

On the other hand, according to yet another example of the presentinvention, application of the method for constituting a virtual RBbundle may be decided according to usage of the second slot under thecondition that R-PDCCH (or DL grant) is detected in the first slot of acertain RB pair.

For example, assuming that a PDSCH is transmitted in a second slot of anRB pair in which R-PDCCH (or DL grant) is transmitted in a first slot,this means that the R-PDCCH and the PDSCH share DMRSs transmitted overtwo slots. Therefore, the RB pair in which PDSCH is transmitted in asecond slot is incorporated into a conventional RB bundle (or RB bundlefor a PDSCH) although R-PDCCH (or DL grant) is transmitted in the firstslot, such that channel estimation can be performed on the assumption ofthe same precoding and/or the same power allocation as in theconventional RB bundle (i.e., RB pairs contiguous to the correspondingRB pair). That is, if PDSCH is allocated to the second slot of a certainRB pair, channel estimation can be performed on the assumption of thesame precoding and/or the same power allocation on the basis of an RBbundle for a PDSCH, irrespective of whether R-PDCCH (or DL grant) istransmitted in the first slot. In other words, it is assumed that thesame precoding is applied to all RB pairs to which PDSCH is allocated,so that channel estimation can be performed on this assumption.

On the other hand, assuming that PDSCH is not transmitted in a secondslot of the RB pair in which R-PDCCH (or DL grant) is transmitted in afirst slot (for example, assuming that a UL grant or no signal istransmitted in the second slot), this means that the R-PDCCH and thePDSCH do not share a DMRS transmitted over two slots. In this case, itis not assumed that the same precoding and/or the same power allocationare/is allocated to R-PDCCH and PDSCH. Therefore, the RB pair in whichR-PDCCH (or DL grant) is transmitted is not incorporated into the RBbundle for a PDSCH, such that channel estimation can be performed usingthe virtual RB bundle shown in one of FIGS. 16 to 19.

In other words, according to the above-mentioned description, the RNuses an RB bundle composed of only RB pairs in which PDSCH istransmitted, and channel estimation is performed on the assumption thatthe same precoding and the same power allocation are used in thecorresponding RB bundle.

Channel Estimation Dependent Upon SCID Setting

A scrambling identify (SCID) may be applied to create a DMRS sequence.The SCID used in DMRS sequence creation may be indicated to a receiverthrough a DCI format configured to schedule DL transmission. Forexample, SCID may be set to 0 or 1 and may be differently assigned toindividual antenna ports so as to distinguish antenna ports.

In a backhaul downlink from the eNB to the RN, the same SCID may beassigned to R-PDCCH and PDSCH, or different SCIDs may be assigned toR-PDCCH and PDSCH. In more detail, while the same SCID may be assignedto DMRSs transmitted in the R-PDCCH region and DMRSs transmitted in thePDSCH region, it should be noted that different SCIDs may be assignedthereto. For example, although R-PDCCH and PDSCH are transmitted throughthe same antenna port index (e.g., antenna port index 7), SCID used forthe R-PDCCH is fixed to zero (0) and SCID used for PDSCH may beindicated by ‘SCID=1’ through control information in the R-PDCCH. Inthis case, R-PDCCH and PDSCH may be transmitted in the same RB bundle asshown in FIG. 22, and may be assigned different SCIDs. Detailed examplesof the channel estimation operation according to the above-mentionedembodiments of the present invention will hereinafter be described indetail.

In accordance with one example of the present invention, it is assumedthat the same precoding and/or the same power allocation are/is appliedto R-PDCCH and PDSCH having different SCIDs, and channel estimation canbe performed on this assumption. That is, although the SCID assigned tothe R-PDCCH is different from SCID assigned to the PDSCH, the same powerallocation and/or the same precoding are/is applied to signalstransmitted through the same antenna port within the same RB bundle.Accordingly, the RN can perform channel estimation for one RB bundleusing more DMRSs (i.e., DMRSs for the R-PDCCH region and DMRSs for thePDSCH region), such that channel estimation performance can be improved.

According to another example of the present invention, in the case wheredifferent SCIDs are assigned to R-PDCCH and PDSCH, channel estimationcan be performed in the RB bundle other than an RB pair including theR-PDCCH. In more detail, although signals are transmitted through thesame antenna port within the same RB bundle, if the signals havedifferent SCIDs, this means that it is improper to apply the assumptionof the same precoding and/or the same power allocation. If it is assumedthat channel estimation is performed as described above, channelestimation performance is lower than that of the above-mentioned example(assuming different SCIDs and the same power allocation and/or the sameprecoding), but the channel estimation operation over different SCIDsneed not be used, thereby simplifying a configuration related to thereceiver of the RN.

On the other hand, in the case where the SCID of the PDSCH is indicatedas the same value as that of the R-PDCCH through control information inthe R-PDCCH, it is assumed that the same power allocation and/or thesame precoding are/is applied to the R-PDCCH and the PDSCH, and channelestimation is performed on this assumption.

FIG. 23 is a flowchart illustrating an exemplary DL channel estimationoperation of a relay node (RN).

The overall operations of the eNB and the RN will hereinafter bedescribed with reference to FIG. 23. Steps S2310 to S2340 shown in FIG.23 are performed by the eNB. In more detail, the eNB assigns an R-PDCCHfor transmitting DL control information to DL resources, assigns a PDSCHfor transmitting DL data to DL resources, and maps DMRSs to DLresources. One or more of the steps S2310 to S2340 may be simultaneouslyperformed. DL control information, DL data and DMRSs, that are assignedand/or mapped to DL resources in steps S2310 to S2340, are transmittedto the RN, such that the RN can receive the control information, the DLdata, and the DMRSs. According to whether a PDSCH is allocated to aspecific RB pair to which R-PDCCH is allocated in DL resources, the RNmay perform channel estimation using DMRSs of an RB bundle used as aunit of DL channel estimation, and demodulate and decode DL controlinformation and DL data on the basis of the estimated channel.Individual operations shown in FIG. 23 will hereinafter be described indetail.

In step S2310, the eNB may include an R-PDCCH in one RB pair (first RBpair). For example, R-PDCCH may include DL grant control information.R-PDCCH may be assigned to a first slot of the first RB pair. Inaddition, PDSCH may be assigned to a second slot of the first RB pair,or R-PDCCH transmitting UL grant control information may be assigned tothe second slot of the first RB pair. Alternatively, no signal (i.e., anull signal) may be assigned to the second slot of the first RB pair.

The eNB may map DMRSs to the first RB pair in step S2320. The DMRS maybe mapped to the first RB pair according to a DMRS pattern dependentupon the number of layers (i.e., ranks) in which R-PDCCH and/or PDSCHassigned to the first RB pair are/is transmitted.

In step S2330, the eNB may assign a PDSCH to one or more RB pairscontiguous to the first RB pair. In step S2340, the eNB may map DMRSs toone or more RB pairs to which PDSCH is assigned at step S2330. The DMRSsmay be mapped to each RB pair according to a DMRS pattern dependent uponthe number of layers (i.e., ranks) in which PDSCH assigned to the one ormore RB pairs is transmitted.

In step S2350, the eNB transmits DL control information, DL data, and/orDMRSs to the RN, such that the RN can receive those from the eNB. The DLcontrol information, the DL data and/or the DMRSs transmitted in thefirst RB pair and one or more RB pairs contiguous to the first RB paircan be transmitted in the same time unit (e.g., one subframe).

In step S2360, in order to determine an RB bundle for channelestimation, the RN may determine whether a PDSCH is assigned to thefirst RB pair to which a DL grant R-PDCCH is assigned. Since channelestimation can be performed on the assumption that the same precoder isapplied to the RB bundle, it is necessary to determine which RB pair iscontained in one RB bundle. In other words, the RN according to thepresent invention may determine an RB bundle for channel estimation bydetermining whether a PDSCH is assigned to the first RB pair in whichR-PDCCH is assigned.

If the RN determines that the PDSCH is assigned to the first RB pair towhich the R-PDCCH is assigned in step S2360, the RN determines RB pairs(i.e., the first RB pair and one or more RB pairs contiguous to thefirst RB pair) to which the PDSCH is assigned to be one RB bundle, andperforms channel estimation on the assumption that the same precoder isapplied to the corresponding RB bundle in step S2370. Channel estimationcan be performed using all DMRSs transmitted in the corresponding RBbundle.

For example, the RB bundle including the first RB pair may be applied tochannel estimation of each of the one or more layers (e.g., layerindexes 0 and 1) used for transmitting the R-PDCCH assigned to the firstRB pair. On the other hand, for channel estimation upon individuallayers (e.g., layer indexes 2 to 7) that are not used for transmittingthe R-PDCCH assigned to the first RB pair, but used for transmitting thePDSCH assigned to one or more RB pairs contiguous to the first RB pair,the RB bundle including RB pairs other than the first RB pair may beused as a channel estimation unit.

Alternatively, the RB bundle including the first RB pair may be appliedto estimate a DL channel under the condition that the number of DLlayers assumed for decoding the R-PDCCH assigned to the first RB pair isat least a predetermined number (e.g., 3). On the other hand, if thenumber of DL layers is less than the predetermined number, the RB bundleincluding the RB pairs other than the first RB pair may be used as achannel estimation unit.

If it is determined that the PDSCH is not assigned to the first RB pairto which the R-PDCCH is assigned in step S2360, the RB bundle includingRB pairs other than the first RB pair to which the R-PDCCH is assignedis decided, and channel estimation can be performed on the assumptionthat the same precoder is applied to the corresponding RB bundle. Thechannel estimation may be performed using all DMRSs transmitted in thecorresponding RB bundle.

In step S2380, the RN demodulates R-PDCCH and/or PDSCH on the basis ofthe estimated channel of the step S2370, and it can receive DL controlinformation and/or DL data.

In FIG. 23, in association with the method for estimating a DL channelof the RN, details described in the above-mentioned various embodimentsmay be applied independently, or two or more embodiments may besimultaneously applied. Redundant matters will not be described hereinfor clarity.

In addition, although the above-mentioned various embodiments of thepresent invention have disclosed MIMO transmission between the eNB andthe RN, the scope of the present invention is not limited thereto, andit is obvious to those skilled in the art that the principle proposed inthe present invention can also be applied to any DL transmission entity(eNB or RN) and any DL reception entity (UE or RN) without departingfrom the scope of the invention. For example, proposed principle relatedto DL transmission from the eNB to the RN may also be equally applied toother types of DL transmission from the eNB to the UE or from the RN tothe UE. For example, proposed principle related to DL reception by theRN from the eNB may also be equally applied to other types of DLreception by UE from the eNB or by UE from the RN. In more detail, inthe case where a DL reception entity demodulates a control channel(e.g., an advanced PDCCH) for the corresponding DL reception entityusing a DL channel estimated by DMRSs within a certain RB pair, andreceives control information, the above-mentioned embodiment canestablish an RB bundle assuming the application of the same precoder,and the principles of the present invention can also be applied to theabove-mentioned embodiment.

FIG. 24 is a block diagram of an eNB apparatus and an RN apparatusaccording to an embodiment of the present invention.

Referring to FIG. 24, an eNB apparatus 2410 may include an Rx module2411, a Tx module 1212, a processor 2413, a memory 2414, and a pluralityof antennas 2415. The plurality of antennas 2415 supports MIMOtransmission and reception. The reception (Rx) module 2411 may receive avariety of signals, data and information on an uplink starting fromeither the UE or the RN. The Tx module 2412 may transmit a variety ofsignals, data and information on a downlink for the UE or the RN. Theprocessor 2413 may provide overall control to the eNB apparatus 1410.

The eNB apparatus 2410 according to one embodiment of the presentinvention may be configured to transmit a DL signal for the RN. Theprocessor 2413 of the eNB may be configured to transmit DL controlinformation through an R-PDCCH within a first RB pair through the Txmodule 2412, and may also be configured to transmit a demodulationreference signal (DMRS) used for estimating a DL channel used fordemodulating the R-PDCCH. In addition, through the Tx module 2412, theprocessor 2413 may be configured to transmit DL data through a PDSCHwithin one or more RB pairs contiguous to the first RB pair, and mayalso be configured to transmit a DMRS used for estimating a DL channelused for demodulating the PDSCH. In addition, in the case where thePDSCH is assigned to the first RB pair, the processor 2413 may apply thesame precoder to one RB bundle including one or more RB pairs contiguousto the first RB pair.

Besides, the processor 2413 processes information received at the eNBapparatus 2410 and transmission information. The memory 2414 may storethe processed information for a predetermined time. The memory 2414 maybe replaced with a component such as a buffer (not shown).

The RN apparatus 2420 may include an Rx module 2421, a Tx module 2422, aprocessor 2423, a memory 2424, and a plurality of antennas 2425. Theplurality of antennas 2425 indicates an RN for supporting MIMOtransmission and reception. The Rx module 2421 may include a first Rxmodule and a second Rx module. The first Rx module may receive downlinksignals, data and information from the eNB. The second Rx module mayreceive uplink signals, data and information from the UE. The Tx module2422 may include a first Tx module and a second Tx module. The first Txmodule may transmit uplink signals, data and information to an eNB. Thesecond Tx module may transmit downlink signals, data and information tothe UE. The processor 2423 may provide overall control to the UEapparatus 2420.

The RN apparatus 2420 according to one embodiment of the presentinvention may be configured to estimate a DL channel starting from theeNB in a wireless communication system. The processor 2423 of the RNapparatus 2420 may demodulate an R-PDCCH of a first RB pair on the basisof a DL channel estimated by a DMRS of the first RB pair and receive DLcontrol information through the first Rx module. In addition, throughthe first Rx module, on the basis of a DL channel estimated by a DMRS ofone or more RB pairs contiguous to the first RB pair, the processor 2423may demodulate a PDSCH of the one or more RB pairs so as to receive DLdata. If the PDSCH is assigned to the first RB pair, DL channel may beestimated on the assumption that the same precoder is applied to one RBbundle including the first RB pair and the one or more RB pairscontiguous to the first RB pair.

The processor 2423 of the RN apparatus 2420 processes informationreceived at the RN apparatus 2420 and transmission information. Thememory 2424 may store the processed information for a predeterminedtime. The memory 2424 may be replaced with a component such as a buffer(not shown).

The specific configurations of the above eNB and RN apparatuses may beimplemented such that the various embodiments of the present inventionare performed independently or two or more embodiments of the presentinvention are performed simultaneously. Redundant matters will not bedescribed herein for clarity.

Although FIG. 24 has exemplarily described MIMO transmission between theeNB and the RN, the same description of the eNB apparatus 2410 shown inFIG. 24 is applicable to any DL transmission entity (eNB or RN), and thesame description of the RN apparatus 2420 is applicable to any DLreception entity (UE or RN). For example, the eNB apparatus configuredto transmit a downlink signal to the RN shown in FIG. 24 may also beequally applied to an eNB for transmitting a downlink signal to the UEor to an RN for transmitting a downlink signal to the UE. In addition,the RN apparatus configured to receive a downlink signal from the eNBmay also be equally applied to a UE for receiving a downlink signal fromthe eNB or to a UE for receiving a downlink signal from the RN. In moredetail, when implementing the downlink reception entity that receivescontrol information by demodulating a control channel (e.g., an advancedPDCCH) of the corresponding DL reception entity using the DL channelestimated by a DMRS within a certain RB pair, the present invention canestablish the RB bundle on the assumption of the same precoder in such amanner that the principles of the present invention can be equallyapplied to all embodiments of the present invention.

The above-described embodiments of the present invention can beimplemented by a variety of means, for example, hardware, firmware,software, or a combination of them.

In the case of implementing the present invention by hardware, thepresent invention can be implemented with application specificintegrated circuits (ASICs), Digital signal processors (DSPs), digitalsignal processing devices (DSPDs), programmable logic devices (PLDs),field programmable gate arrays (FPGAs), a processor, a controller, amicrocontroller, a microprocessor, etc.

If operations or functions of the present invention are implemented byfirmware or software, the present invention can be implemented in theform of a variety of formats, for example, modules, procedures,functions, etc. The software codes may be stored in a memory unit sothat it can be driven by a processor. The memory unit is located insideor outside of the processor, so that it can communicate with theaforementioned processor via a variety of well-known parts.

The detailed description of the exemplary embodiments of the presentinvention has been given to enable those skilled in the art to implementand practice the invention. Although the invention has been describedwith reference to the exemplary embodiments, those skilled in the artwill appreciate that various modifications and variations can be made inthe present invention without departing from the scope of the inventiondescribed in the appended claims. For example, those skilled in the artmay use each construction described in the above embodiments incombination with each other. Accordingly, the invention should not belimited to the specific embodiments described herein, but should beaccorded the broadest scope consistent with the principles and novelfeatures disclosed herein.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the essential characteristics of the presentinvention. The above exemplary embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein. Also, it will be obvious to those skilled in theart that claims that are not explicitly cited in the appended claims maybe presented in combination as an exemplary embodiment of the presentinvention or included as a new claim by subsequent amendment after theapplication is filed.

The embodiments of the present invention are applicable to variousmobile communication systems. It will be apparent to those skilled inthe art that various modifications and variations can be made in thepresent invention without departing from the scope of the invention.Thus, it is intended that the present invention cover the modificationsand variations of this invention provided they come within the scope ofthe appended claims and their equivalents.

What is claimed is:
 1. A method for receiving a downlink signal at adownlink reception entity in a wireless communication system, the methodcomprising: receiving downlink control information by demodulating aPhysical Downlink Control Channel (PDCCH) in a first resource block (RB)pair within an RB bundle by using a first Demodulation Reference Signal(DMRS) in the first RB pair; and receiving downlink data by demodulatinga Physical Downlink Shared Channel (PDSCH) in one or more second RBpairs within the RB bundle based on channel estimation performed using asecond DMRS in the one or more second RB pairs, wherein the second DMRSis used for the channel estimation based on an assumption that a sameprecoder is applied to the one or more second RB pairs within the RBbundle except the first RB pair.
 2. The method of claim 1, wherein thedownlink control information includes downlink scheduling informationassociated with the PDSCH.
 3. The method of claim 1, wherein the PDSCHis not mapped to resource elements used for the second DMRS.
 4. Themethod of claim 1, wherein the RB bundle includes consecutive RB pairs.5. A downlink reception entity for performing downlink reception, thedownlink reception entity comprising: a reception module configured toreceive a downlink signal from a downlink transmission entity; atransmission module configured to transmit an uplink signal to thedownlink transmission entity; and a processor configured to control thereception module and the transmission module, wherein the processor isfurther configured to: receive, through the reception module, downlinkcontrol information by demodulating a Physical Downlink Control Channel(PDCCH) in a first resource block (RB) pair within an RB bundle by usinga first Demodulation Reference Signal (DMRS) in the first RB pair; andreceive, through the reception module, downlink data by demodulating aPhysical Downlink Shared Channel (PDSCH) in one or more second RB pairswithin the RB bundle based on channel estimation performed using asecond DMRS in the one or more second RB pairs, wherein the second DMRSis used for the channel estimation based on an assumption that a sameprecoder is applied to the one or more second RB pairs within the RBbundle except the first RB pair.